Glossary_text

EWG SEA ICE ATLAS GLOSSARY

INTRODUCTION

PREFACE TO THE 1994 RUSSIAN EDITION

Any field of science, and ice science is no exception, has its own terminology, i.e., a set of terms, words and expressions, which continuously develops and becomes more perfect. This development is determined by specific sources of terms and a number of other factors, such as the growing scope of scientific research, the integration of different fields of science, and international co-operation.

It is well known that the first system for sea ice classification was developed in the USSR in 1921 – 1928 and that a new edition of this system was approved in 1938. After World War II, the use of new methods for monitoring and research (ice surveys, aerial photography of ice) catalyzed a rapid increase in both new data and knowledge concerning sea ice behavior and processes. This resulted in the creation of new terms and concepts related to ice and made it necessary to review existing terminology because "the old classification system and terminology could not meet the new requirements" [22].

With a view toward developing new terminology, the Interdepartmental Ice Committee was established in 1952. In 1954, "Classification and Terminology of Ice Existing in the Sea" was approved and submitted for review to the Oceanographic Committee of the USSR Academy of Sciences. The Classification was also discussed and approved at scientific council sessions of the Arctic and Antarctic Research Institute (AARI) and the State Oceanographic Institute (SOI).

Late in the 60s, the World Meteorological Organization (WMO) undertook the task of reconciling sets of terms and classification systems of ice as well as the sets of symbols and methods for representing ice related information that existed in different countries. As a result, in 1967, the Interdepartmental Committee for Sea Ice was established in the USSR and studied various proposals and submitted them to WMO. In 1968, the Interdepartmental Committee put forth a draft Soviet ice terminology glossary which, for unknown reasons, was called "International Ice Nomenclature". The document not only contained lists of terms used in ice science, as the word "nomenclature" would imply, but in fact was a complete terminology dictionary with its own terminology and classification system. The final version of "International Nomenclature" was published in the USSR in 1974 and was implemented in March 1974 by the Hydrometeorological Service (currently Rosgidromet) as well as by other agencies and organizations of the USSR.

In accordance with the resolution of the Council of Ministers of the USSR (no. 16 of 11.01.65), the introduction of International Nomenclature was accompanied by work aimed at the standardization of scientific and technical terminology and notations used in technology, as well as in technical literature, regulatory documents, and industry.

In accordance with the state plan for standardization, SOI began the development of the draft State Standard "Oceanology. Terms and Definitions" in 1969. Although one section of this Standard, "Sea Ice", was developed at AARI at that time, this work was never completed.

In 1977, the Ice Terminology Committee of the International Association on Hydraulic Researches (IAHR) compiled a dictionary which contained 106 terms relating to the construction and operation of hydrotechnical structures under ice conditions in fresh-water areas. However, intense exploration of the shelves of the arctic seas occurring at that time brought up the question of expanding and developing the dictionary to also include terminology used in ice covered marine areas. As a result, this dictionary was also never published.

Understandably, the question of streamlining terminology has been a top priority in all stages of the development of ice science. However, no practical research has been carried out in this field. As a rule, terminology problems have been addressed in general research works such as monographs, manuals, and instructions. In this connection it should be noted that different authors often have quite different interpretations of similar terms. For instance, the interpretation of some terms such as relative ice area, state of the ice sheet, and ice conditions, often varies. In contrast to the terminology related to ice sheet state, which was included in World Ice Nomenclature published in 1974, terms which originated in the process of investigating ice properties and ice regimes, ice navigation, and the construction of hydrotechnical objects are scattered through the literature. For instance, ice forecasting terminology can be found in two manuals [29, 34].

At present, there does not exist a common glossary of the terminology associated with the scientific study of sea ice. Furthermore, in 1984 the "International Notations for Sea Ice Maps and Nomenclature of Sea Ice" was published, resulting in the effective annulment of the bulk of the prior USSR terminology. As a result, there is at present no Russian national system of terminology and classification of either fresh-water ice or sea ice.

During the last 15 to 20 years, in both Russia and abroad, a great number of investigations have been undertaken concerning the physical, mechanical, and chemical properties of ice. For instance, the scope of investigation of the ice regime of fresh-water bodies has been considerably expanded. Ice forecasts and ice regime monitoring are now often based on numerical methods of analysis and prediction, based on mathematical models of the various processes occurring in ice. The use of such models is impossible without an adequate classification of ice- related phenomena and processes. Rapid increases in the number of investigators have also increased the number of "individually created" concepts and terms which are not the result of new scientific achievements but many times are the result of insufficient understanding of the subject. At the same time, clear definitions of many important generic notions (for example, ice sheet, ice regime, ice conditions, etc.) still have to be proposed.

The present glossary of sea ice terminology is a first attempt to systemize in one- volume terms related to ice and its properties, to the properties of ice sheets, to ice forecasting, and to the scientific and operational support of ice navigation.

This first draft version of this glossary has been sent to a number of Departments of Rosgidromet and to other organizations involved in activities connected with sea ice. The authors received a large number of comments and proposals – most of which were taken into account when preparing the glossary for publication. In particular, the authors agreed with the suggestion that an alphabetic ordering of terms and notions be utilized. However, in some cases, the authors found it more logical to use hierarchical principles in establishing the order of headings, similar to that used in the Nomenclature of Sea Ice proposed by WMO.

The order of the terms in this dictionary was determined by the principles listed below:

? each term must create a logical link to the notion defined and should not contradict it;

? each term must have its own well defined place in the terminological system in question;

? one must be able to use the term to form new terms;

? terms must not be long and should be melodious if possible;

? terms must be unique, multiple meanings must be excluded; and

? terms must be easily translatable into foreign languages.

As this glossary is not encyclopedic, the authors have used definitions as the main method for introducing terms. Extended definitions are only given in cases of very important concepts or when a more complete discussion is warranted.

In their work on the glossary the authors used a large number of reference books, regulations and instructions, and national and foreign literature on sea ice. Many of these reference sources are listed at the end of this document.

The authors wish to thank the following colleagues for their assistance: Doctor of Science (geography) A. Ya. Buzuev; cand. sci. (physics and mathematics) B. Ya. Gaitskhoki; Doctor of Science (geography) Yu. A. Gorbunov; cand. sci. (geography) V. D. Grishchenko; Doctor of Science (geography) V. V. Panov; cand.sci. (geography) V. I. Fedotov; cand. sci. (geography) I. E. Frolov; and cand. sci. (geography) N. V. Cherepanov.

We also wish to thank V. I. Shilnikov, K. M. Kumachev, V. D. Grishchenko and others who helped us in preparing photographs.

Naturally, this glossary, can not cover all the terms that exist in the field of sea ice science. The authors assume that some terms may be missing. We shall be grateful for any further suggestions regarding improvements, omissions, and errors. We look forward to hearing from users of this dictionary, whether or not they have words and definitions to add.

PREFACE TO THE 1998 ENGLISH EDITION

We have attempted to keep the English edition of this glossary as close to the Russian original as possible. Although the exact wording may not always be the same, we have also attempted to make our definitions consistent with the sea ice terms listed in the World Meteorological Organization’s "Sea Ice Nomenclature" [31, 46]. In the few cases where in our view there are differences between real-world usage and the more formal WMO definitions, we have noted these in our comments. There are also a number of cases where a direct translation of a Russian word or phrase into English is very different than the correct English translation. In that it is not uncommon to see the direct instead of the correct terms in documents prepared by non-specialists, we have dealt with this problem by providing the direct translation and then adding the correct English phrase in brackets in the associated text [e.g. FúHJRJCVQXTCRBT directly translates to aerocosmic which refers to what is called remote sensing in English]. We have also added a number of references from the English literature to the reference list to further assist the reader. A comparison with the original Russian edition of this glossary will also show that there have been major changes in the photographs used as illustrative material. This was the result of the fact that many of the original prints were no longer available. Fortunately we have been able to fill this void through the generosity of several individuals and organizations. Full photo credits are given after the bibliography.

We regret that we did not have the pleasure of the assistance of Captain of the First Rank Kazanskii in preparing this translation as he died in 1994.SUGGESTIONS ON THE USE OF THIS GLOSSARY

In preparing this glossary we have had to make a number of decisions concerning the arrangement of the expressions discussed here. The result is a combination of an alphabetical and hierarchical arrangement. As will immediately become obvious on the following page, the main arrangement of terms is alphabetical. We have also used alphabetical sequences in the listing of many of the subsets of the main terms. This is invariably true when these terms do not fall into some natural sequence. When they do, such as objects having a natural size or age sequence, we have listed them according to that sequence. To avoid the endless repetition of definitions, we have not repeated many of the definitions that naturally occur as part of a subset of other definitions. However, in the index we have listed all the terms that have been referred to in the text regardless of their location.

We suggest that persons searching for a particular definition should start the search in the index and then proceed to the particular page listed. If that approach does not immediately produce the desired term, you should look for your term attached to the word ice; for example, ice crystals, ice draft, ice forecasting, ice keel, etc. We also think that the reader will find it interesting to browse through the book discovering the surprisingly diverse maze of terminology that has developed in the rather specialized field of sea ice studies. Happy hunting and good luck.

A

ABLATION OF SNOW AND ICE ( ). A decrease in the mass of snow and ice due to melting and evaporation.

ABSOLUTE ELONGATION OF ICE. See deformation of ice; absolute deformation.

ACCESSIBLE SPEED DURING VESSEL NAVIGATION IN ICE. The maximum speed that a vessel can achieve under specific ice conditions. Its value is primarily determined by the dimensions and shape of the vessel and the power of vessel’s engine.

ACCURACY OF ICE FORECASTS. An averaged error of forecasts, drawn up using a given forecasting method.

ACTIVE ICE LAYER. The surface layer of an ice sheet that is subjected to periodic melting and refreezing. At medium latitudes during the spring melt season, the development of such a layer depends on the temperature change during the day while in old ice at high latitudes it depends on the intensity of seasonal melting and refreezing.

ACTIVE RADIO DETECTION OF ICE. The remote sensing of an ice sheet with the help of electromagnetic waves. Radio detection is typically carried out by irradiating sea ice with electromagnetic waves and then analyzing the nature of the return.

At present, pulse and phase-frequency modulation methods are commonly used in the investigation of sea ice by radio detection. Radio probing of ice is based on the ability of electromagnetic waves to penetrate ice and be reflected at boundaries where there is a change in electromagnetic properties.

ACTUAL ICE NAVIGATION TIME. The period of time between the date when the first cargo vessel arrives on a given route and the date when the last vessel leaves it.

ADHESION OF ICE. The freezing of ice to foreign bodies due to the forces of intermolecular attraction. The adhesive strength (per unit area) is measured in terms of the force applied to, or the work performed on, an area of ice necessary to detach it from the associated (typically flat) surface of the other material.

ADIABATIC MODULUS OF ELASTICITY. The modulus of elasticity measured under the condition of adiabatic deformation. For instance, adiabatic conditions occur during the propagation of elastic waves when the oscillatory displacements of particles are rapid enough so that the heat exchange with the environment during the period of one oscillation is negligible. The adiabatic modulus of elasticity can be calculated with reasonable accuracy with the help of the following formula:

where E is the normal elastic modulus, is the adiabatic modulus of elasticity, a is the thermal expansion coefficient, Cp is the specific heat capacity at constant pressure, and T is the ice temperature.

The difference between the adiabatic and the isothermal elastic moduli of ice is very small (only 0.1% in the case of fresh-water polycrystalline ice at a temperature of -10°C). Therefore the above term is not frequently used.

ADVECTION OF ICE. The movement of ice in a horizontal direction without any essential changes in the compactness or other properties of the ice.

AGE OF AN ICE SHEET. The period of time between the initial formation of a relatively homogeneous level continuous part of an ice cover and the time of the current observations. Qualitative terms describing the relative age of ice as indicated by its thickness are initial, black, young, one-year old and old ice.

INITIAL ICE. A primary, usually not compact layer of ice needles and plates, ice and snow crystals or ice-snow porous clumps that are lightly frozen together. The age of initial ice is expressed in hours and the thickness of initial ice does not exceed 5 cm.

Grease ice. A layer of ice needles and plates that has thickened somewhat in the course of freezing and is typically distributed over the water surface in the shape of strips or small spots. Because of its matte surface, grease ice usually appears to have a dead grayish color ( Photograph 1).

New snow ice. A layer consisting of a viscous mass of water saturated snow ( Photograph 2).

Slush ice (interwater ice). An agglomeration of primary needle-shaped and lamellar crystals formed within the surface water layer as the result of supercooling.

BLACK ICE (NILAS). A thin (up to 5 cm), elastic layer of ice showing a dark color. It is easily flexed by water waves. When compressed, it commonly rafts forming toothed or keyboard-like overlapping layers referred to as finger rafts ( Photograph 3).

Dark ice. A rotten, snow-free ice cover (less than 5 cm thick) showing a wet brine-covered surface. This ice type develops from initial ice.

Light ice. Opaque-grayish snow-free ice (5-10 cm thick) showing numerous air-holes of various shapes.

Pancake ice. Young ice accumulations with a round or oval shape in the horizontal plane and typical diameters of 0.3 to 3.0 m. Pancakes typically have raised edges in the form of accumulations of brash ice and ice crystals which are produced as a result of oscillations between adjoining pancakes caused by waves and swell ( Photograph 4). Frequently the formation of pancakes is preceded by the formation of glass ice which is then broken by swell and rounded into pancakes by intra-floe contacts.

Glass ice. A transparent crust of breakable fresh-water ice (up to 5 cm thick). Glass ice is typically rigid and brittle.

YOUNG ICE. Gray, thin ice (10 - 30 cm thick), which is easily flexed by waves. Under compression its layers commonly raft over one another ultimately forming stable unbroken multi-layered ice sheets ( Photograph 5). The age of young ice varies from several hours to 25 - 30 days depending on the geographic location and the local climatic conditions during a given year.

Gray ice. Young ice with thicknesses up to 10 - 15 cm that commonly shows a gray-colored surface and contains a few round-shaped air holes. Gray ice is both less wet and less brittle than glass ice. Upon compression, its layers raft over each other, though they are also capable of hummocking. If hummocks form, they can reach heights of 10 - 15 cm.

Gray-white ice. Young gray ice with thicknesses between 15 - 30 cm that presents a grayish-white, comparatively level surface which may retain a thin snow layer. When compressed it typically forms hummocks rather than rafts. The average heights of such hummocks are 16 - 32 cm (45-50 cm at maximum).

FIRST-YEAR ICE. This is a general expression referring to white ice during its first year of existence ( Photograph 6) . Ice thicknesses by the end of the winter can vary over a wide range with values between 30 - 250 cm; the exact value depends on the time of initial ice formation and on the climatic conditions in that region during the applicable time period. Commonly the snow cover on first-year ice is comparatively stable showing specific patterns of dunes and snow ridges. Fractures and cracks which may develop into leads are also common. Under compression first-year ice can develop a variety of deformation features (ridges, hummocks, ice barriers and belts). During the melt period, its surface is covered with snow melt pools, small thaw lakes and channels, which exhibit specific patterns for each first-year ice type.

First-year thin ice. Gray-white ice which is 30 - 70 cm thick. Fresh fractures are a white color. Dunes and snow ridges are elongated in the predominant wind direction. As a result, thawing sets up an elongated pattern of melt pools and small thaw lakes. Hummocks are normally 30 - 75 cm high with maximum values reaching 100 cm. In most cases hummock ridges are linear, whereas fresh fractures extend along zigzag lines. At some locations two stages of first-year thin ice can be distinguished with the first stage being 30 - 50 cm thick while the second stage is 50 - 70 cm thick.

Medium thick first-year ice. First-year ice with thicknesses from 70 to 120 cm. In non-Arctic seas, this type of first-year ice represents the limit of ice growth for extremely severe winters. The surfaces of fresh fractures are light-greenish in color. Snow ridges and dunes may be elongated in several directions. Many hummock ridges intersect, with hummock heights reaching 175 cm. This ice-type usually melts completely during the Arctic summer.

First-year thick ice. First-year ice with thicknesses ranging from 120 to 250 cm. The surfaces of fresh fractures have a greenish tinge. This ice is quite strong and only hummocks under very intense compressive stresses. Hummocks are typically 1.5 – 2.5 m high, and in some cases 3.2 – 3.5 m. A stable snow cover characteristically develops and displays a complicated pattern of dunes and snow ridges. During the thaw period, large numbers of small thaw lakes and water patches develop near the edges of hummocks.

OLD ICE. Ice that has survived melting during at least one summer. Such ice is usually covered with a thick layer of snow. Melt-smoothed hummocks, which can survive for many years, are gradually transformed into hills and hillocks. The thaw pools that normally develop from snow melt are usually rounded in outline. The color of old ice varies from greenish to light blue.

Residual first-year ice. The initial stage of the two-year ice cycle. In the northern hemisphere this stage lasts from the moment of new stable ice formation until the 1st of January or until the 1st of July in the Southern hemisphere. Residual first-year ice is similar in appearance to first-year thick ice during the period of maximum melting.

Second year ice. Sea ice during its second-year, i.e. sea ice that has survived one summer but not two. Fresh fractures are greenish - light-blue in color. The near surface layer is mostly desalinated (unlike more saline first-year ice). This ice type is distinguished by the following morphometric characteristics: higher freeboards, more rounded and uneven upper surfaces, and hummocks with typically smaller horizontal dimensions. Hummocking takes place only under very strong compression. Floes are normally edged with hummocky formations which have developed from young or first-year thin ice ( Photograph 7). Thawing produces rounded , 5461 thaw pools ( Photograph 8) and a few thaw patches.

Multiyear ice. Sea ice that is over two years in age. Such ice is typically made up of rounded floes that have hilly upper surfaces that originate by irregular melting during multiple thaw cycles ( Photograph 9). The height of the surface topography is 1.5 - 2.5 meters. This ice type is usually covered with compact snow and is normally light blue in color. This color is typical for the so-called paleocrystic ice which occurs in the Canadian parts of the Arctic. During summer, the surface of paleocrystic ice develops rounded melt pools. Its surface drainage systems are typically well developed ( Photograph 10).

Pack ice (pack). This term used to be applied to multiyear ice (sometimes it is still used that way). For instance, Canadian pack ice is in fact multiyear ice which originated in the Canadian Arctic archipelago. However, current usage of the term pack ice does not refer to the age of the ice but only to the fact that it is not fast but is drifting as the result of atmospheric and oceanic stresses applied to its upper and lower surfaces ( Photograph 11).

AGE OF HUMMOCKY FORMATIONS. Qualitative estimates of the relative age of hummocky formations as determined by the overall shapes of their above-water portions, the degree of bonding between and the amount of rounding of the blocks within the hummocks, and the nature of the associated snow cover.

FRESH HUMMOCKY FORMATIONS. Newly developed, snow-free hummocky formations with sharp tops and ridges whose above-water slopes are typically 35 - 40° ( Photograph 10). Ice fragments and ice debris both on the surface and under water retain their initial angular shapes. Widths in new hummocky formations commonly exceed heights by 7-8 times. The ratio of the draft of hummock ridges to their sail height as measured relative to sea level is 5 : 1 ( Photograph 12).

SMOOTHED HUMMOCKY FORMATIONS. Hummocky formations with the ridges rounded by ablation and the above-water slopes leveled. Average slope angles are 25 - 30°.

OLD HUMMOCKY FORMATIONS. Hummocky formations resembling chains of hills, considerably smoothed and solidified ( Photograph 13).

AGGREGATE OF ICE CRYSTALS. A group of parallel-fibre crystals that show similar crystallographic orientations relative to the arrangements of the basal (0001) plane. The occurrence of such aggregates is typical of sea ice that has formed in the absence of appreciable wave action and under conditions where a stable, presumably steady directional current exists ( Figure 1).

AIR CONTENT IN AN ICEBERG. The volume content of air bubbles in an iceberg expressed as a percent of total volume. The air content of icebergs ranges from 1 to 15% by volume.

AIR HOLE. A hole in an ice sheet that has formed as a result of either natural or artificial processes. Air holes of natural origin mostly occur in black and young ice as the result of convection in the underlying seawater ( Photograph 14). Artificial air holes are made by sawing or cutting out pieces of ice and removing the fragments until a hole results.

AMORPHOUS ICE. Ice possessing no organized crystal structure. Amorphous ice is formed when vapor condenses on surfaces maintained at temperatures below -160°C.

ANISOTROPY OF MECHANICAL PROPERTIES OF ICE. Such anisotropy results from the fact that several types of crystal structures which naturally occur in sea ice can result in directionally dependent physical and mechanical properties.

Pure polycrystalline ice is distinguished by two types of "initial" anisotropy: textural anisotropy, determined by the form and arrangement of the crystal boundaries and structural anisotropy, determined by preferred C-axes crystallographic orientations. In contrast to "initial" anisotropy, which exists from the initial time of ice formation, ice may also develop induced anisotropy through deformation processes which result in recrystallization which manifests itself through shifts and rotations of individual crystals.

Sea ice sheets are also characterized by so-called transverse anisotropy in their properties (i.e., the upper part of the ice has properties that are different from that of the lower part of the ice). For instance, the fact that the upper part of the ice is usually colder than the lower part explains the differences in the in-situ cantilever beam strength as measured when the load is applied upwards causing the initial tensile failure to occur in the weaker (warmer) ice at the bottom of the sheet or is applied downwards causing the initial failure to occur in the stronger (colder) ice near the top of the sheet ( Figure 2).

ANNUAL BEHAVIOR OF ICE COVER ELEMENTS. The changes in the value of an ice sheet element during one year. The annual behavior of an ice sheet element is determined either on the basis of data averaged over many years of observations or on the basis of data obtained during a given year.

ATMOSPHERIC ICE. Ice formed on a surface of an object from atmospheric water (sometimes, from the fallen snow).

AUTHOR’S LAY-OUT OF AN ICE MAP. The geographical lay-out (rough) of an ice map designed by the author without complying with the requirements of accuracy and design.

AUTONOMOUS NAVIGATION OF A VESSEL (ICEBREAKER) IN ICE. The navigation of a vessel (icebreaker) through an ice-covered region without assistance from other vessels (icebreakers).

AUXILIARY ICEBREAKING VESSEL. A specialized towed vessel designed for icebreaking operations. Such vessels may be used in combination with either a cargo vessel or an icebreaker.

B

BARCHAN. A snow dune having a crescentic shape in plan view with both the concave side and the steeper slope facing downwind. This type of dune is occasionally seen occurring on the surface of flat ice.

BARE ICE. Ice with a snow-free surface.

BARRIER OF STRANDED LANDFAST ICE. See fast ice; shore ridge

BASAL PLANES OF AN ICE CRYSTAL. Planes oriented perpendicular to the optical or C-axis of an ice crystal ( Figure 1).

BASAL PLATE. A conventional name for the elementary plates ( Figure 1) which constitute an ice crystal and are arranged perpendicular to the optic or C-axis.

BEARING CAPACITY OF ICE SHEET. See Supporting power of ice sheet.

BLACK ICE. (NILAS).

1. A thin (up to 5 cm) elastic layer of ice on the water surface, dark in appearance and easily flexed by waves. When compressed it can flex into small folds which then freeze into place as ice surface features ( Photograph 15). When black ice breaks and the separated pieces come back into contact under pressure, rafts consisting of keyboard-like overlapping layers referred to in English as finger rafts commonly occur.
2. The ice formed due to the freezing of fresh water pools containing very small amounts of scattering impurities. This ice has a dark and almost black appearance and corresponds to ice types A1, A2, and A3 in Cherepanov’s classification ( Figure 3).

BORDER OF ICEBERG SPREADING. A boundary (usually on a map) separating the maximum observed equatorward locations where icebergs have been sighted from more southerly locations where icebergs have never been sighted.

BRASH ICE ZONE. Parts of an ice sheet consisting of crushed and ground-up fragments of ice either surrounding large ice-floes or located between them. Brash ice zones may comprise 30 - 35% of the total area of an ice field.

BRINE IN ICE. The liquid solution of sea salts contained in the ice at temperatures below 0°C. This brine typically occurs in the form of liquid inclusions of different sizes and shapes which are commonly elongated in the vertical direction.

BRITTLE STRENGTH OF ICE. See Strength characteristics of ice.

"BROWN" ZONES. Changes in the color of sea water in the vicinity of icebergs and along the front of shore glaciers in the Antarctic, usually attributed to intense biological activity.

C

CARGO VESSEL ICE CERTIFICATE. A document specifying a vessel’s navigation speed through ice based on qualities such as its ice-crossing capacity, ice-resisting strength, maneuverability in ice, and availability of special equipment and systems. The particular ice conditions that will be encountered will also be considered.

CATACLASIS OF ICE. See fragmentation of ice.

CHANNEL See also Lead.. A widened main crack. Channels can be subdivided into narrow (50 - 200 meters wide), medium (200 - 500 meters wide), and wide (widths of over 500 meters). Traditionally, channel definitions also include the strip of open water (in some cases filled with ice fragments) left by the transit of an icebreaker or a vessel through ice ( Photograph 16 ). [In English the term channel is used primarily to refer to the open water areas produced by or utilized by shipping while cracks that have become sufficiently wide that they cannot be jumped are called leads].

CLASSIFICATION OF ICE FORECASTS. Ice forecasts are classified according to their objectives, term, stages, content, as well as other features.

CLASSIFICATION OF FORECASTS BY PURPOSE

SYSTEMATIC ICE FORECASTS. Ice forecasts that are prepared on a regular basis and within fixed time periods by operative divisions using approved forecasting methods.

SPECIAL ICE FORECASTS. Ice forecasts prepared by operative divisions at the request of specific consumers of forecasting information. Special forecasts commonly are focused on a particular problem or on a region or time period where forecasts are not routinely provided.

CLASSIFICATION OF FORECASTS BY FORECASTING OBJECTIVES

RIVER ICE FORECASTS. Ice forecasts prepared for rivers, their estuaries and for coastal areas affected by river water.

SEA ICE FORECASTS. Ice forecasts for seas or their parts (regions) and for the Arctic Ocean and Antarctic seas.

CLASSIFICATION OF FORECASTS BY FORECASTING STAGES.

PRELIMINARY ICE FORECAST. An ice forecast prepared prior to the main ice forecast. A preliminary ice forecast is prepared on the basis of limited information and prognostic dependencies that give bigger errors. Therefore such forecasts have a somewhat tentative character.

MAIN ICE FORECAST. The first ice forecast for every parameter or characteristic of the structure, state or composition of an ice sheet. It also characterizes the evolution of an ice sheet. A main ice forecast is prepared in accordance with the ice forecast schedule. The term of forecast preparation, as well as its form and content are established on the basis of a special agreement concluded between the forecasting organization and the customer.

ICE FORECAST CORRECTION. An ice forecast adjusting an earlier main ice forecast. Ice forecast corrections may be prepared in accordance with the forecast preparation schedule or whenever necessary depending on the rate or intensity of ice process development and the need to adjust earlier forecasts regarding some phenomena or processes.

EMERGENCY (EPISODIC) ICE FORECAST. An ice forecast prepared in the case of a customer’s emergency request.

CLASSIFICATION OF FORECASTS BY TERM

SHORT-TERM ICE FORECASTS. Detailed ice forecasts with a term of several hours to 3 days.

MEDIUM-TERM ICE FORECASTS. An ice forecast with a term of 3 to 15 days.

LONG-TERM ICE FORECASTS. Ice forecasts with a term of 15 days to 6 months.

SUPER-LONG-TERM ICE FORECASTS. Ice forecasts with a term of 6 months to several years.

CLASSIFICATION OF FORECASTS BY THEIR CONTENT

FORECAST OF THE START OF ICE FORMATION. An ice forecast that contains information on the expected time of initial ice formation. This forecast is prepared for separate regions, localities, or for the whole area of a water body. In the latter case, the ice forecast is prepared in the form of a prognostic map showing the isochrones indicating the start of stable ice formation.

FORECAST OF THE ACHIEVEMENT OF A SPECIFIED THICKNESS. An ice forecast that contains information on the expected times when the thickness of young ice reaches 5 - 10 and 20 - 25 centimeters. Beginning from this moment, navigation requires the use of icebreakers.

ICE THICKNESS FORECAST. An ice forecast that contains information on the expected thickness of ice on a specified date.

FORECAST OF ICE THICKNESS AT THE START OF MELTING. An ice forecast that contains information on the expected maximum thickness of ice in a specified locality.

FORECAST OF THE TIME OF FAST ICE BREAK-UP AND OF THE FINAL DESTRUCTION OF THE ICE. An ice forecast that contains estimates of the expected time of initial break-up of the fast ice as well as the time of complete break-up of fast ice and the formation of drifting ice.

FORECAST OF ICE COVERAGE. An ice forecast containing information on the expected (for a given moment of time or averaged over some period of time) amount of ice, including all types of ice occurring in a given part of the sea or water area irrespective of the ice’s age, compactness, and other parameters.

FORECAST OF ICE MASSIF AREA. An ice forecast containing information on the expected (for a given moment of time or averaged over a specified period of time) area of ice fields having a compactness of 7 - 10 points.

ICE DISTRIBUTION FORECAST. An ice forecast containing information on the expected location of an ice field’s edge as well as boundaries separating ice fields with different values of compactness and age. Such forecasts also commonly contain information on the character of development and the state of large discontinuities in an ice sheet such as air-holes and clearings.

FORECAST OF THE DEGREE OF BREAK-UP. An ice forecast containing information on the expected time when a specified degree of break-up will occur in the ice in a given locality or region.

ICE DRIFT FORECAST. An ice forecast providing information on the projected direction, speed, and total distance of expected ice drift during a specified time period. Such forecasts are prepared on the basis of prognostic maps of air pressure, isobaric coefficients, and the values of angles of an ice drift deviation from the isobars. An ice drift forecast can also be prepared on the basis of information on the direction and velocity of wind, data on wind coefficients, and representative angles between drift and wind directions typical for a given region and time of year. Preparation of such forecasts also requires a knowledge of the ocean currents in the forecast area.

ICE COMPRESSION FORECAST. An ice forecast providing information on the wind-driven compression of ice in a given area of a sea or along a sea route. This forecast also takes into account the results of calculations of tidal compression and decompression.

CLASSIFICATION OF ICEBERGS BY AGE

YOUNG ICEBERGS. Blocks of continental ice that have split off from a glacier a short time ago and have a typical angular shape.

OLD ICEBERGS. Icebergs subject to melting and destruction in their above- and under-water segments (as well as at their waterlines).

Old icebergs often drift in a state of unstable equilibrium and may suddenly turn over or split.

CLASSIFICATION OF ICEBERGS BY COLOR

BLACK-AND-WHITE OR STRIPED ICEBERGS. Icebergs containing large quantities of unevenly distributed coarse morainic material.

BLACK ICEBERGS. Icebergs whose surface is covered with sand, rocks and other material picked up from the sea floor when the iceberg rolled over.

BLUE ICEBERGS. Glacier icebergs which sometimes contain fragments of continental rock. The blue color is the result of the fact that ice selectively transmits light in the blue frequency range while absorbing at other frequencies.

DARK-GREEN ICEBERGS. Icebergs with heterogeneous inclusions which do not appear on the surface. The exact nature of the inclusions, although still problematic, is believed by some to be biologic material. Such icebergs are rare and are most frequently sighted at locations off the Antarctic continent.

WHITE ICEBERGS. Firn or shelf icebergs with a well developed stratification and exhibiting a white color.

CLASSIFICATION OF ICEBERGS BY LOCATION

ANTARCTIC ICEBERGS. Icebergs of all types formed from the Antarctic ice sheet and drifting in the Southern hemisphere.

DRIFTING ICE ISLANDS. A class of icebergs existing in Arctic waters. They calve from the ice shelf located along the northern coast of Ellesmere Island and, possibly, from a glacier on Axel Heiberg Island. Drifting ice islands have freeboards of 5 - 15 m and drafts of 30 m.

The surface areas of ice islands range from several thousand square meters up to 500 square kilometers. Icebergs of this type usually are composed of strongly layered ice ( Photograph 17) and have upper surfaces that show large elongated undulations ( Photograph 18).

EAST-GREENLAND ICEBERGS. Large icebergs with average heights of 50 - 60 meters. The maximum heights of these icebergs may reach 120 meters and the maximum draft 150 meters.

EURASIAN ICEBERGS. Icebergs existing in the Arctic seas. The height of Eurasian icebergs ranges from 5 to 25 meters, their length - from 100 to 150 meters, and draft - from 50 to 60 meters, and in a few cases- up to 100 meters.

WEST-GREENLAND ICEBERGS. Icebergs of a very large size. The heights of West-Greenland icebergs range from 215 - 225 meters while drafts may reach 500 meters. Their length may be over 1500 meters ( Photograph 19).

CLASSIFICATION OF ICEBERGS BY SHAPE

ARC AND CAVE ICEBERGS. Icebergs whose above-water portions have partially collapsed forming an arc or cavern ( Photograph 20). Icebergs of this type are often characterized by well developed rams.

CRUSHING OR CRUMBLING ICEBERGS. These icebergs can exist in a variety of different forms. However, their above- and below-water sections show a considerable degree of decay due to melting and mechanical destruction in the vicinity of the waterline. Crumbling icebergs may have complicated, exotic forms.

DOCK ICEBERGS. Icebergs with a broken middle part in the form of a V-shaped groove flanked with double pyramids.

DOME-SHAPED ICEBERGS. Icebergs with dome-shaped upper surfaces. Dome-shaped icebergs form as a result of ice blocks calving from outlet glaciers.

RIBBED ICEBERGS. Icebergs covered with parallel grooves which form a ribbed surface. The depths of grooves and distance between them are approximately 20 cm. Ribbed icebergs have only been reported in Southern waters.

ROUNDED ICEBERGS. In high latitude waters, these icebergs have rounded shapes which develop as the result of slow melting and weathering. In other parts of the World ocean, rounded icebergs appear to be produced by the repeated rolling of other types of icebergs.

TABULAR ICEBERGS. Icebergs with horizontal top and bottom surfaces and vertical side walls. Tabular icebergs are formed when large-sized blocks of ice split off from ice shelves ( Photograph 21).

TILTED ICEBERGS. Icebergs which resemble a tilted slab with one end submerged in water. Tilted icebergs represent a transitional stage between tabular and glacier icebergs ( Photograph 22).

TURNED-OVER ICEBERGS. Icebergs which have rolled as the result of instabilities produced by shape changes caused by melting and the calving of fragments.

WING-SHAPED AND HORN-SHAPED ICEBERGS. Icebergs whose shapes formed under the influence of prolonged melting and weathering. Wing- or horn-shaped icebergs represent the last stages of an iceberg’s existence ( Photograph 23).

CLASSIFICATION OF ICEBERGS BY SIZE

PIECE OF ICEBERG. A small monolithic piece of fresh-water ice up to 1.5 meters high by up to 1.7 meters wide, and up to 2.5 meters long.

FRAGMENT OF ICEBERG. A block of ice split off from an iceberg and located near it, often called a "cub" or a "puppy". Its above water dimensions are 1.8 - 5.0 meters wide, 2.6 - 7.5 meters long, and 1.6 - 3.0 meters high.

SEGMENT OF ICEBERG. A part of an iceberg 5 - 15 meters high, 5 - 10 meters wide, and 7.5 - 15 meters high.

SMALL ICEBERG. A block of fresh-water ice 5 - 15 meters high, 10 - 40 meters wide, and 15 - 60 meters long.

MEDIUM ICEBERG. A block of ice 16 - 30 meters high, 41 - 85 meters wide, and 61 - 130 meters long.

LARGE ICEBERG. A block of ice 30 - 50 meters high, 86 - 130 meters wide, and 131 - 200 meters long.

GIANT ICEBERG. A very large iceberg more than 50 m high, 230 m wide and 200 m in length.

COEFFICIENT OF DYNAMIC VISCOSITY OF ICE. The coefficient of dynamic viscosity of ice h is defined by the decrement d in the mechanical oscillations of an ice sample when measured at a frequency f and with the elastic modulus E:

> > > > > > > h = d ´ E / (2 p 2 ¦)

Values of h calculated using the parameters of damped oscillations are 5 to 6 orders larger than static viscosity coefficients corresponding to the plastic flow of ice.

COEFFICIENT OF ICE THERMAL CONDUCTIVITY. See thermal conductivity of ice.

COEFFICIENT OF LIGHT REFLECTION BY ICE. The ratio of the reflected intensity to the intensity of the incident light wave.

In meteorology, an ice sheet is characterized by an albedo - a photometric parameter that characterizes the ability of a matte (dull) ice surface to reflect (scatter) the incident light flux. The albedo of an ice surface is defined by the ratio of reflected radiation to that of incident radiation.

COEFFICIENT OF WIND-DRIVEN DRIFT OF ICE. The ratio of the drift velocity of the ice to that of the wind causing the drift. Average values of this parameter for the Antarctic basin are equal to 0.02.

COMPACT ICE EDGE. A comparatively narrow transition zone comprised of compact ice located between open water and a region of pack ice having a different compactness ( Photograph 24).

CONDITIONAL-INSTANT ICE STRENGTH. See brittle strength of ice.

CONGELATION. This term refers to the formation of ice by the direct freezing of bulk water. More specifically the expression congelation ice refers to ice that has grown from bulk water or seawater as the result of the latent heat of freezing being conducted upward through the overlying ice to the atmosphere.

CONTINENTAL ICE. Ice formed on the land as a result of accumulation and transformation of different types of solid atmospheric precipitation.

CONTINUOUS NAVIGATION OF A VESSEL. The forward movement of a vessel through specified ice conditions without stopping.

CONVERGENCE OF ICE. See divergence of ice.

CONVOY NAVIGATION WITH RARE (FREQUENT) ICE BREAKING. Convoy navigation under complicated ice conditions that result in the occasional (frequent) complete stopping of the vessels and that require the utilization of ice breaking services by the ice-breaker in order for the convoy to continue further movement.

COVE IN ICE An area of open water that deeply penetrates into an ice field resulting in the formation of a concavity along the ice edge.

COVERAGE OF VESSELS WITH ICE. The formation of a snow/ice cushion in the area where the vessel’s body directly contacts the ice. The formation of such a snow/ice cushion results either in a decrease in the vessel’s speed or in a full stop.

CRACKS (IN AN ICE SHEET). Any fracture in fast ice, consolidated ice or in a single floe that has a width of less than 1 m ( Photograph 25). [In field usage, if the fracture is narrow enough for one to jump across, it is a crack. If it cannot be jumped, it is a lead.] Cracks are formed in ice sheets as a result of the accumulation of stresses that exceed the strength of the ice. Such cracks can be are subdivided in accordance with their genetic and morphologic features:

The shape along their lateral extent - straight (linear, wedge, slot-type), bent (arc, link, round-type), fractured (zigzag, sinusoidal, cycloid-type) (picture 38).

The shape of crack edge - smooth, uneven, notched.

The length - intrablock (up to 5 km long), interblock (up to 100 km long), main (some hundreds of kilometers long).

The penetration depth - gaping, unopened.

The age - fresh (cracks containing either clear water or primary ice types), young (cracks covered with young ice), old (cracks covered with winter ice) (picture 39).

ISOSTATIC CRACKS. Cracks that form as the result of unbalanced loads from hummocks, their ridges or barriers, as well as from artificial loads.

PEELING CRACKS. The cracks that form on the border of the divide between winter ice and either old or black or young ice when the tensile strength of these latter ice types is higher than the cohesive strength of the bond attaching them to the stronger winter ice.

SHIFT CRACKS. Cracks that can develop in black ice and in other young ice types that have formed in existing leads and channels, open water areas and pools as the result of relative shifts in the positions of adjacent ice floes.

SLIDE-APART CRACKS. Cracks formed in the ice sheet as a result of bilateral compression.

SLIP CRACKS. Cracks formed in winter ice in zones where shearing is occurring.

SPLIT CRACKS. Cracks formed in an ice sheet due to compression in locations where sharp-edged protuberances of hummock ridges or extending capes of stronger ice types are encountered.

TEAR-OFF CRACKS. Cracks occurring due to the elongation of black ice or young ice, and also in ice sheets that show significant spatial heterogeneity.

THERMAL CRACKS. Cracks formed in the upper layers of an ice sheet as the result of thermal stresses produced by rapid changes in ice temperature usually resulting from rapid changes in air temperature.

TIDAL CRACKS. Cracks that form in fast ice as a result of flexural deformation that occurs associated with the rise and fall of the tides. Tidal cracks form along coast lines and also around stranded ice features such as stamukhi and other grounded obstacles.

WAVE CRACKS. These cracks form near the edges of ice sheets as the result of the effect of waves and swell. They consist of stretched longitudinal and short crossing cracks that form a polygonal pattern on the ice sheet .

CROSS-ICE CAPACITY OF A VESSEL. The ability of a vessel to move under specific ice conditions. The cross-ice capacity of a vessel under given ice conditions is expressed in terms of its speed.

CRYSTALLINE HOARFROST (RIME). Fresh-water atmospheric ice which forms from water vapor in the air on the surface of an object (Photograph 26).

CRYSTALLIZATION OF WATER. The formation of ice crystals as a result of the ordering of water molecules into the structure of the hexagonal phase Ice I. The details of the resulting crystals (shapes, sizes, orientations, etc.) depend on the cooling rate and the thermodynamic conditions of the water body.

CRYSTALLIZATION NUCLEI. Small (10-7 – 10-3 cm) particles of mineral and organic origin whose surfaces assist in the nucleation of ice crystals from supercooled water.

CRYOHYDRATE. A mechanical mixture of ice crystals and solid salt crystals in which the latter was precipitated at temperatures below 0°C.

CURVE OF ICE LONG-TERM STRENGTH. A dependence between the stress ss and the time to failure ts which can be developed from a set of creep curves ( Figure 4, see also Limit of Long-Term Ice Strength). This dependence is a convenient method for describing the longevity of an ice sample placed under a given load.

For some types of fresh-water and sea ice, the following relations between ts and ss are known:

where A, n, l, and s¥ are rheologic parameters derived from data obtained through experiments on the uniaxial compression of ice or from experiments on the in situ compression of ice with the help of a down-hole expansometer. ( Figure 5).

> > > > > > > > D

DEFORMATION MODULUS OF ICE. The ratio of stress to the relative change in the size of a sample in the direction of the force. This term was introduced to ice science by V.V. Lavrov in order to more clearly distinguish the true modulus of elasticity of ice from its quasi-properties observed during prolonged deformation in static compression or tension experiments. The apparent elasticity moduli obtained in these experiments are calculated with the help of formulae from the strength of materials theory relating ice deformation to the imposed stress. Apparent moduli are called the flexural deformation modulus, the compression deformation modulus (modulus of dilatation) and the tensile deformation modulus. These parameters strongly depend on many factors, including the experimental method used and the dimensions of the sample.

Because the behavior of ice under tension and compression is different, the flexural deformation modulus is a reduced (effective) modulus and can be expressed in terms of the elasticity modulus for compression Ecomp and the elasticity modulus for tension Etens:

It is obvious that when Ecomp = Etens, Ered = Ecomp = Etens

Therefore, the reduced modulus of elasticity is obtained if one assumes that the material behaves in the same way whether it is subjected to compression or tension. In this connection, we recommend that experimental data on deformation moduli available in the literature not be used unless the exact experimental conditions are described.

DEGREE OF ICE COVERAGE WITH SNOW. A parameter characterizing the degree of ice surface coverage with snow. It is defined by the ratio of the area of snow-covered ice to the total area of an ice sheet. It is typically assumed that the distribution pattern of snow-covered areas is uniform.

DEGREE OF ICE SHEET POLLUTION . A parameter characterizing the degree that an ice sheet is polluted. It is defined as the ratio of the area of polluted ice to that of ice characterized by a uniform distribution of pollutants and it is measured in points.

DE-ICING OF A WATER AREA. The disappearance of ice from a part or the whole of a water area due either to the complete melting of the ice or to its drifting away from the area under observation leaving open water.

External evidence that the de-icing process is underway is the thinning of the ice sheet, a process that can continue until the sheet disappears as the thickness becomes zero. However, in most cases, thinning is associated with decreases in concentration and with associated lateral melting as well as with increased movement of the ice. The sea ice in the foreground of Photograph 19 is in the last stages of the de-icing process.

DESALTING (DESALINATION) OF SEA ICE. The process or processes by which the amount of sea salts in the ice decreases.

DESTRUCTION OF THE ICE SHEET. The process by which a uniform ice sheet is broken up under the effect of external forces resulting in a decrease in the horizontal dimensions of compact ice formations.

DESTRUCTIVE ICE LAYER. A layer of an ice sheet with a structure resulting from selective internal melting caused by penetrating solar radiation. Typically such layers are in the upper part of the ice sheet.

DIRTY ICE. Any ice type which contains a sufficient amount of mineral or organic inclusions on either its surface or internally to cause the ice to have a dirty appearance ( Photograph 28).

DISCHARGE OF ICE STRESS. A sharp decrease of stress in a local ice volume with no obvious change in its continuity near the sites where the detectors are installed.

In the case of drifting ice fields, dynamic cracking will commonly be the source of such stress discharges, and in the case of thermal effects - thermal cracks. Stress discharges may be measured by a stress detector or a strain gauge installed in the ice. In the latter case, the discharged stress Ds is defined by the equation:

where e is the relative discharge deformation and E is the modulus of elasticity of the ice.

DIVERGENCE OF ICE. The term divergence refers to a differential characteristic of a vector field that is used to describe the relative drift velocities of ice. The divergence characterizes the variation of the displacement vector in the vicinity of an observation point. It belongs to the class of volume derivatives of vector fields:

,

where vx, vy, and vz are the vector projections of the drift velocity V onto the coordinate frame axes.

A positive divergence signifies an increase of an ice area due a decrease in compactness as the floes move further apart. This is usually associated with a lowering of the in-ice stress. A negative divergence (convergence) indicates that the area of an ice field is decreasing as the floes move closer together. Convergence is typically accompanied by deformation such as ridging and rafting and/or an increase in the degree of compactness and in the in-ice stress..

DRIFT DIVIDE. A linear, elongated area containing finely fragmented ice-floes ( Photograph 53). The drift divide area separates two ice fields or an ice field and fast ice and is characterized by a rapidly changing drift velocity gradient. Due to a decrease in compression, the drift divide may develop cracks, pools of open water and, in some cases, areas of rarefied ice. Drift divides can be areas of intense deformation ( Photograph 59)

DYNAMIC SEA ICE. Sea ice of hydrospheric origin which accumulates on objects due to the freezing of splashes and droplets of sea-water having a salt content by weight of more than 24.7 pro mille (‰). This ice type characteristically occurs as the result of the collision of waves with the marine structures.

DYNAMO-ELASTIC PARAMETERS OF ICE. A set of experimental characteristics measured by observing the elastic behavior of ice (i.e. when the load is applied for a time that is sufficiently short so that the time of loading does not exceed the stress relaxation time). Dynamo-elastic parameters of ice are obtained on the basis of experimental values of velocities of longitudinal and transverse waves where the velocities are measured by high-frequency acoustic methods.

E

EASIEST WAY OF ICE NAVIGATION. The vessel route through a region of ice chosen in order to obtain the most favorable overall combination of ice sheet properties (thickness, compactness, hummockness, degree of destruction of the ice, etc.).

ECONOMIC EFFECT OF ICE FORECAST. The estimate of consumer usefulness and economic reasonability of using an ice forecast to implement production functions in economic industries that depend on ice conditions.

EDDY MOTION OF ICE. A motion of ice where the ice floes perform translation motions and simultaneously rotate around a temporarily fixed point.

ANTICYCLONIC MOTION OF ICE. A clockwise eddy motion of the ice, e.g. the anticyclonic circular motion of ice in the Arctic basin (according to data on ice drifts averaged over an observation period of several years, one year or one season). Note that when Arctic Basin data is averaged over a shorter time period, other motion preferences may be indicated.

CYCLONIC MOTION OF ICE. A counterclockwise eddy motion of the ice.

EDGE OF SHORE ICE. A line separating an immobile ice sheet (shore ice, landfast ice) from open water or moving pack ice (Photographs 11 and 53).

EFFECTIVENESS OF ICE FORECAST. The ratio of the effect of its use to the total amount of charges for all forecasting stages.

ELASTIC MODULI OF ICE. Elastic moduli are parameters that characterize the elastic properties of ice.

Under conditions of small deformations, the most general relationship between the components of stress sxx, syy, ... sxy and the components of strain exx, eyy, exy are presented in the form of six linear equations of the type

where sxx is a so-called normal stress which is directed along the x axis, tyz is the tangential or shear stress in the plane whose normal is parallel to y, eyz is the relative shear, (i.e., the change in the value of the right angle of elementary parallelepiped in a plane yz), etc. The coefficients c11, c12,.... are elasticity moduli or the constants of rigidity and have dimensions of stress, i.e. are expressed in terms of units of force divided by units of area.

For hexagonal crystals there are only five independent moduli of elasticity known as the rigidity constants. These parameters, (c11, c12, c13, c33, c44), appear as coefficients in the equation relating the components of the stress tensor to the components of the strain tensor.

The physical meaning of the elasticity moduli can be understood by considering the main types of stressed ice states – uniaxial normal stress, shear deformation, and triaxial compression. The relation between stress and the corresponding strain is in each case presented in the form of a simple formula where stress is the product of the corresponding strain and the elasticity modulus.

ELEMENTS OF MACRORELIEF OF AN ICE SHEET (COVER) SURFACE. Comparatively stable aggregates of large structural unevenness as observed on the surfaces of sheets of sea ice or on the ice cover as a whole. Typical sizes fluctuate from a few meters to several tens of meters.

ENSEMBLES (SETS) OF ICE COVER ELEMENTS. Groups of ice floes of different shapes and sizes which either partially or completely cover the surface of a water body

EQUILIBRIUM ICE THICKNESS. The thickness of old drift ice. Ideally the thickness at which the winter’s growth is completely compensated by the summer’s melting and evaporation. In arctic regions, the equilibrium ice thickness is on the average equal to 3 m, but occasionally may reach 5-6m.

ERROR OF LONG-TERM ICE FORECASTS WITH TIMELINESS UP TO 2 MONTHS. The error that does not exceed ± 0.674s.

ERROR OF LONG-TERM ICE FORECASTS WITH TIMELINESS FROM 2 TO 6 MONTHS. The error that does not exceed ± 0.8s.

ERROR OF SUPER-LONG-TERM FORECASTS. The error that does not exceed the average quadratic error of a forecast event.

Here Ui is the parameter value or the ice sheet indicator arranged in multi-year observation rows, Up is the calculated value of the forecast parameter or indicator, d is the deviation of calculated values from the actual ones d = (Ui - Up), n is the number in a multi-year row, and m is the number of degrees of freedom (for a linear regression equation m = 2).

ESTIMATE OF ICE FORECAST QUALITY. The defining of their accuracy, reliability, justifiability, and efficiency.

EVOLUTION OF AN ICE SHEET (COVER). Gradual changes (trends) in the properties and components of an ice sheet (cover) with time ( Figure 2).

F

FABRIC DIAGRAM OF CRYSTAL AXIS ORIENTATIONS. A diagram that shows the results of measurements of the C-axes orientations of crystals as usually observed in a thin section.

FAST ICE. Sea ice which is attached to the shore (Photographs 11 and 53) or to grounded ice features such as shamuhka ( Photograph 54) or icebergs. Although fast ice may move up and down with the tides and may undergo small lateral movements, when considered on a larger scale it is essentially fixed in place. It may form in situ or be comprised of ice of any age that has drifted into its present location before becoming incorporated in the fast ice. Fast ice widths can vary from a few meters to 100s of kilometers.

FAST ICE BORDER. The line separating shore ice from drifting ice (Photographs 11 and 53).

FAST ICE FORMATION. Fast ice formation occurs along the coasts of continents, archipelagos, and islands and also around old stranded sea ice masses and icebergs on shoals.

The formation of fast ice can be described in terms of four dates: the date of the first off-shore ice occurrence (the day when a stable ice sheet appears along the coast with the width of the strip of less than 200 m); the date of the first fast ice formation (the day when the fast ice is more than 200 m wide and formed along the coastal line); the date of stable fast ice formation ( the day when the stable ice sheet is more than 200 m wide and formed near the coast or other immobile objects such as stamukhi); the date of the final fast ice formation (the day when a stagnant ice sheet has formed over the whole surface of the water area of interest and has existed there for either a period of over one month or during the entire winter period until break-up).

FIRN. Firn is infiltrated as well as recrystallized medium to coarse-grained snow. It typically has densities in the range of 450 to 800 kg/m3 and represents a transition stage between snow and ice of infiltration origin.

"FLOAT" OSCILLATIONS OF ICE. The vertical movement of ice as a whole. The oscillation period depends on the ice thickness.

FLOE. A continuous, connected, relatively flat area of drifting ice with horizontal dimensions ranging from 20 m to dozens of kilometers and vertical dimensions ranging from several centimeters to several meters. Floes are usually classified according to horizontal extent as follows:

Small: 20-100 m across

Medium: 100-500 m across

Big: 500-2000 m across

Vast: 2-10 km across

Giant: over 10 km across

FLOODED ICE. A part of an ice sheet that is covered with a water layer that has formed either due to the melting of snow and ice on its surface, the inflow of water onto the ice from the shore, or the depression of the ice surface below sea level by factors such as snow loading or non-isostatic forces.

FLUCTUATIONS OF ICE DRIFT. Deviations of ice drift parameters from their average values caused by a variety of factors

FOAM ICE. A frozen aqueous foam usually resulting from layer-by-layer freezing of a foamed cold water solution containing a dispersion of surface-active substances.

FORECASTING OF ICE EVENTS AND PROCESSES. The scientific and research process aimed at understanding the physical basis of mechanisms occurring in ice events and processes that define the limit of their predictability, the development of forecast procedures, and their formalism.

FORECASTING PREREQUISITES. The possibility of resolving forecast tasks defined by specific features of an ice event or process, the level of its study, information support, timeliness, and the method of forecast.

Forecasting timeliness. The time defined by the predictability of the process, i.e. the possibility to receive a forecast of required accuracy under existing conditions.

Event study level. The knowledge of factors that directly or indirectly influence the process or event, as well as the availability of the reason/consequence linking the events of different levels in the past, present, and future.

PREDICTABILITY LIMIT. The maximum possible timeliness of a forecast defined by the studied mechanisms of processes linking the ice sheet with meteorological, hydrological, and heliogeophysical processes.

Forecast timeliness. The time period between the submission of the forecast and the start of the time for which it was developed.

FORECASTING STAGES. The consequence of performing certain operations that define the scientific and research process of developing ice forecasts and that include the setting of targets, the selection and compiling of a system of predictors, the development of a constructive forecast model, the development of a specific forecast procedure, and a verification of the forecast.

Setting of forecasting tasks. A forecasting stage that includes the analysis of properties and specific features of ice events and processes, as well as the selection of a suite of indicators that are believed to have significant predictive capabilities concerning the particular problem at hand, the selection of the order with which to use this information, and the setting of forecast timeliness.

Preforecast analysis. A forecasting stage that includes the selection of potential predictors on the basis of theoretical ideas concerning mechanisms and reasonable links in the interaction between physical events and the forecasting process, information support of predictors and the predictant, and the existence of reasonable time shifts between predictors and the predictant when retrospective material is used.

Development of constructive forecasting model. A forecasting stage that includes the establishment of mathematical correlations (probability-statistical and thermohydrodynamic). It transfers into a forecast model upon completion of the final optimization of model parameters and the finalization of the model structure.

FORELL BANDING. A thin straight ribbing relating to the location of the edges of the basal plates that can be seen on the surface of some ice crystals. Forell banding is particularly visible under conditions of either ice sublimation or limited melting with the immediate evaporation of the thawed water.

FRACTURE IN AN ICE COVER. SEE Rasvodije (Russ.).

FREEZING OF WATER. The transition of water from the liquid to the solid state caused by the crystallization process.

FREEZING OF A WATER BODY. The formation of a continuous layer of ice on the surface of a water body.

The external evidence of this process is the covering of the water body with a continuous layer of primary ice. The process is characterized by two dates: the day when the first complete freezing occurs (i.e., the day when observations performed under conditions of full visibility show that the area of the water body was covered by a continuous layer of primary ice for the first time in the given year) and the day when the final freezing occurs (the day when observations conducted under conditions of full visibility show that the area of the water body remained covered with a continuous layer of ice for a period of time no shorter than one month).

FRESH SNOW SHEET. A loose, relatively even snow sheet formed from newly-fallen (newly-precipitated) snow.

FROST STEAM or FROST SMOKE. The formation of fog over cracks, channels, leads and air holes resulting from cold air with temperatures below 0°C passing over open water ( Photograph 29).

G

GLADE. A large area of up to 30 km wide, of open or scattered ice formed at the border between the fast ice or the shore or an ice shelf and the drift ice due to a sustained offshore wind (off-fast-ice glade, offshore glade) ( picture 30).

GLAZE (GLAZED ICE). Ice of an atmospheric or hydrospheric origin that covers the surface of an object and consists of rain drops or light spray spattered onto objects from waves ( Photograph 44). Depending on the salinity of the water and the formation mechanism (spray, water spattered by waves) one can distinguish between fresh-water, salty, and sea glaze, and also between wind, wave, slush and drift glaze. Various combinations of the above glaze types are also possible.

GLEN’S FLOW LAW FOR ICE. A power law useful in describing the creep of ice given by

where A depends on the ice temperature, the impurity content, and the crystal orientation as well as other possible factors and n is an exponent varying from 1.5 to 4.2 as the stress changes from 0.1 to 1.5 MPa. It is common to assume n = 3 as a mean value. The temperature dependence of the parameter A is usually expressed in terms of the Arrhenius equation

where Qcreep is the activation energy for creep, T is the ice temperature, R is Boltzmann’s constant and is independent of temperature.

GOUGING OF THE SEAFLOOR BY HUMMOCKY FORMATIONS. The plowing up of the seafloor by the underwater parts of hummocks, ridges and stranded ice masses (Photographs 30 and 31). The depth of the resulting furrows may in extreme cases reach 10 m. In English this process has also been referred to as scoring and scouring.

GRADIENT OF ICE DRIFT SPEED. The change in the ice drift speed per unit distance in a specified direction.

GRANULAR HOARFROST (RIME). Fresh-water ice of atmospheric origin formed from water droplets such as fog -( Photograph 26). It forms on the surfaces of objects.

GROUP VELOCITY OF WAVES IN AN ICE SHEET (VELOCITY OF THE WAVE FRONT). A parameter which characterizes the velocity of non-harmonic (i.e. non-sinusoidal) waves in ice. For a period of time during which the envelope shape of the wave disturbance remains the same with the required accuracy, one may introduce the propagation velocity of the envelope that characterizes the velocity of elastic impulse perturbations in the medium. In a floating ice sheet, its value may be less (normal dispersion) or more (anomalous dispersion) than the phase velocity.

GROWLER. An accumulation of ice blocks, debris and/or an iceberg fragment that extends less than 1 m above the sea surface and normally occupies an area of roughly 20 m2. Growlers can be quite hazardous to shipping as they commonly are not visible on radar and are particularly difficult to sight during storms.

H

HAZARDOUS ICE PHENOMENA. Ice phenomena which may cause damage to facilities located in areas affected by the phenomena.

One should take necessary measures to prevent this damage. Dangerous ice phenomena include events such as the unusually early formation of ice, piling of ice, partial breaking off of shore ice, and the icing of ship superstructures, etc.

EXTREMELY DANGEROUS ICE PHENOMENA. Ice phenomena which, because of their intensity, time of occurrence, duration and affected area may cause considerable damage to objects in affected areas. In case the objects cannot be evacuated, nor protected and if safety precautions are not followed, this type of phenomena may present a real danger to human life.

A sudden increase in the ice drift rate and intensive ice compression along a navigation route ( Photograph 32) are some types of this phenomena.

It should be noted that the critical values of indexes of hazardous and extremely dangerous ice phenomena have yet to be established.

HEAT CAPACITY OF ICE. An important material property required in the investigation of changes in ice temperature as related to changes in the temperature of the environment. The heat capacity of ice gives the quantity of heat needed to increase the temperature of a unit mass of ice by 1°K. The heat capacity of freshwater ice [2.12 kJ/(kg °K) at 0°C] decreases with a decrease in temperature and trends toward zero at 0°K.

HILL. See ice hill

HILLY PATTERN OF MULTIYEAR ICE. The ratio of the area of hilly ice to the total surface area of multiyear ice on which the hills are located. Expressed in points.

HUMMOCK. A separate pile of pieces and fragments of ice on the upper surface of an ice sheet formed due to the compression of ice fields at their contact points ( Photographs 33).

HUMMOCK BARRIER. A large ridge formed by a line of hummocks in the shore fast ice ( Photograph 59). The underwater part of a hummock barrier is partially grounded, thus assisting in stabilizing the shore fast ice.

HUMMOCK BELT. A row of parallel hummock barriers formed as the result of multiple and prolonged compressive hummocking events. Hummock belts are mainly located at the external edge of the fast ice ( Photograph 59). They also occur in straits and drift divide regions.

HUMMOCKNESS OF ICE. A measure for evaluating hummocky ice defined by the ratio of the hummocky ice area to the entire area of the zone where the estimate of the degree of ice coverage by hummocks is being performed. It is expressed on a 5 point scale.

RIDGE HUMMOCKNESS. An ordered ice hummockness in the form of uniformly distributed hummock ridges on the ice sheet surface. It is estimated in accordance with the number of hummock ridges per unit length of the observation zone which should be oriented perpendicular to the direction of the hummock ridges.

NON-UNIFORM HUMMOCKNESS. Chaotically distributed hummocks and their ridges occurring on the surface of an ice sheet ( Photograph 34). It is estimated in the same manner as the general hummockness (in points).

HUMMOCK RIDGE. A extended, chain-like piling of ice fragments on the upper surface of an ice sheet formed due to compression of ice fields along their line of contact. The elements of a hummock ridge include:

HUMMOCK RIDGE HEIGHT. See morphometric characteristics of ice sheet relief; hummock height.

HUMMOCK RIDGE CREST. The topmost part of a hummock ridge ( Figure 14).

HUMMOCK RIDGE FOOT. An imaginary line separating the hummock ridge slope from the surrounding level (non-deformed) surface.

HUMMOCK RIDGE SLOPE. The side walls of hummocks, the lengths of which are measured from the edge to the foot.

ANGLE OF SLOPE. The angle between the hummock ridge slope and the horizontal plane of the ice sheet (the upper surface of level ice).

WIDTH OF HUMMOCK CHAIN. The distance between two slopes measured on the ice surface near the ridge foot.

HYDROGENIC OR CONGELATION ICE (WATER ICE). Hydrogenic ice forms as the result of water freezing. Such ice is analogous to magmatic rocks. It occurs in various shapes and is extremely wide spread in nature.

HYDROMETEOROLOGICAL INFORMATION TYPES

PRIMARY INFORMATION. Data obtained through observations at stations, during expeditions, and from laboratory research. This type of data characterizes hydrometeorological and ice conditions in the area under study at the moment of the observation and serves as a basis for practical decisions concerning sea ice operations. Such data is also used in scientific research and in developing new calculation and forecasting methods.

REVIEW AND ANALYTICAL INFORMATION. Information of this type is obtained through the generalization of primary information and by conducting analytical calculations to characterize the spatial distribution of the ice and the associated hydrometeorological characteristics at given moment of time or for a specified period of time. Such information usually contains at least one of a set of factors that should be considered in the process of determining optimum routes for navigating vessels through ice.

REGULATORY AND REFERENCE INFORMATION. This type of information is obtained through the statistical processing of primary and analytical information and characterizes climatic and statistical hydrometeorological conditions within a given water area and the dynamics of their change. Such information is commonly used as a part of feasibility studies undertaken in connection with large-scale economic projects.

FORECASTING INFORMATION. Forecasting (prognostic) information is obtained by calculations and forecasts and gives scientifically substantiated characteristics of expected phenomena and processes. It also contains recommendations for dealing with conditions that are likely to take place in the future.

NAVIGATIONAL RECOMMENDATIONS. Recommendations from operational units concerning optimum ice navigation routes, coastal station supply timetables, periods when icebreakers will lead during the transit and periods and routings for led vessels not designed for ice navigation.

STORM WARNING. A timely warning of dangerous and extremely dangerous natural phenomena allowing economic and operational organizations to take preventive measures against possible damage resulting from storm wind intensification, unfavorable changes in the wind direction, rapidly worsening ice conditions, sharp rises or falls of water level, and any other hazardous factors not foreseen by the original ice forecast.

HYDRO-THERMODYNAMICS OF ICE. A branch of hydrology and of ice science which studies the laws governing changes in the thermal state of ice, water currents, and water bodies in the presence of ice formation and melting. The main aim of research in the field of ice thermodynamics is to establish the laws governing the processes of ice formation, evolution and destruction as determined by changes in climatic conditions.

HYDROLOCATION IMAGE OF AN ICE COVER. Normally, a black-and-white image on a paper chart or on an electronic monitor which has been obtained through the use of a narrow scanning beam produced by a hydrolocation station (sonar). The antenna of the station is installed on an object that moves: 1) horizontally under the ice sheet at a specified depth (upward-looking side-scan sonar image, Figure 6) or vertically while at a fixed horizontal location (circular scanning sonar). These images allows one to make assessments of the 3 dimensional roughness of the lower surface of an ice sheet thereby determining areas of uneven, level and continuous ice.

HYDROMETEOROLOGICAL SUPPORT. The complex of works performed by Rosgidromet organizations aimed at timely and completely providing economic organizations with hydrometeorological materials obtained using standard techniques and in accordance with approved schedules.

I

ICE AIRFIELD. An ice sheet with a runway and other services necessary to provide for the landing, take off and parking of aircraft.

ICE ALBEDO (SNOW ALBEDO). The parameter characterizing the reflective ability of an ice (snow) surface. It is defined as a ratio of the total energy reflected by the surface to the total energy that falls onto it. The resulting dimensionless value is usually expressed as a percent or fraction.

ICE ACCUMULATION. An ice zone with a high compactness as compared with the surrounding ice, or the ice zone of any uniformity among open water.

ICE ACTIVATION ENERGY. A constant for a specific process and a specific material that describes the number of molecules having sufficient energy to undergo a reaction as a function of temperature. For instance in the literature, one finds the term "activation energy of ice creep" (the energy required for dislocations to move in the creep process) as well as the activation energy of mechanical relaxation, that both correspond to the above definition. Traditionally, this value is designated by the Latin letters Q, U or W. For clear ice, its value is approximately 55kJ/mole.

ICE ATLAS. A systematized collection of ice maps (charts, tables, etc.) arranged in accordance with their purpose, content, and design to form a cartographic atlas.

ICE BALANCE OF A WATER BODY. The ratio of the income/loss of ice on a given water body as established throughout a year or as an average over several years.

Income of ice is attributed to the freezing of water resulting in the thickening of the ice, the formation of hummocks, the transfer of ice from neighboring water areas, the condensation of atmospheric water, and snow.

The loss of ice is caused by melting, evaporation and the removal of ice from a water body.

ICE BARRIER. A relatively immobile edge of an ice shelf or glacier tongue. Height above sea-level typically exceeds 2 meters.

ICEBERG. A large-sized monolithic block of fresh-water ice either free-floating in the sea or grounded at the moment of observation. Icebergs can be as high as 70–100 meters above sea level and have lateral dimensions as large as 100 kilometers or even more. The underwater portion of an iceberg usually constitutes 70% to 90% of its volume. [see Photographs 17, 19, 20, 21, 22, 23]

Icebergs usually calve from the outlets of continental glaciers or ice shelves.

Icebergs calved from outlet glaciers are usually tabular in shape with slightly bulging tops that are divided by various irregularities such as cracks and crevasses. Icebergs of this type are common for Antarctic seas.

The tops of icebergs calved from continental glaciers are almost never level. Instead they are usually tilted and resemble gable roofs. Sizes of icebergs of this type are smaller than sizes of other types of icebergs found in the Antarctic seas.

Icebergs calved from ice shelves normally have large horizontal dimensions (dozens and even hundreds of kilometers). On the average, their height above sea level is 35 - 50 meters. Icebergs of this type have level, horizontal surfaces and almost vertical and level side walls.

ICEBERG HEIGHT. The vertical distance between the highest point of the iceberg and the surface of the sea. In order to determine the height of an iceberg one commonly measures (with the help of a sextant) the vertical angle between the sea surface and the topmost point of the iceberg and also the distance to the iceberg.

The largest icebergs have been found in the Denmark Strait (iceberg height 120 meters); offshore Baffin Island (iceberg height 212 - 225 meters); in Antarctica (offshore Falkland Islands, (iceberg height 450 meters), and at the point with co-ordinates 44°s.lat. and 40°w.long, (iceberg height nearly 510 meters).

ICEBERG LENGTH. The largest straight-line distance between two points located at opposite ends of the iceberg.

ICEBERG WATERLINE. The line of contact between the iceberg and the surface of the water.

STEEPNESS OF ICEBERG SLOPES. The angle between the iceberg slope and the sea surface.

The distance at which an iceberg can be detected with the help of radar greatly depends on the steepness of its slopes. Large icebergs with steep walls can be detected with the help of radar from a distance of 14 - 30 miles. Icebergs with 30° walls (normally found in the northern part of the Atlantic Ocean) can be detected with radar at a distance of 6 - 12 miles. Icebergs with less steep walls are difficult to detect and monitor.

SURF TERRACE (RECESS). A wave-shaped indentation along the windward side of an iceberg formed as the result of wave-induced melting. The development of surf terraces results in icebergs becoming unstable and rolling over. After an iceberg has rolled, a new terrace may begin to develop at a new location. Such cycles may be repeated many times leading to the iceberg floating higher in the water, an increase in the size of the rams, and a change in the shape of the iceberg.

ICEBERG COMPACTNESS. The number of icebergs per unit sea area. The compactness of icebergs is defined by the distance between them in accordance with the following 10-point scale. [21]

Points Number of icebergs Average distance

per 1000 km2 between icebergs, km

0 - -

1 <1 >150-200

2 1-2 30-150

3 3-4 20- 30

4 5-8 15- 20

5 9-16 10-15

6 17-44 6-10

7 >44 2- 6

8 >44 1- 2

9 >44 <1

ICEBERG DEPOSITS. Morainal materials released from an iceberg as a result of thawing and disintegration and subsequently deposited on the sea floor.

ICEBERG DRAFT. The depth of the underwater part of as iceberg measured relative to sea level. Icebergs with the largest drafts (which may be as large as 546 meters) have been found in the North Atlantic Ocean. The underwater part of an iceberg is usually very uneven and sometimes the draft of the bottom surface may vary from dozens to hundreds of meters as the exact point of measurement changes.

ICEBERG HALO. A halo or glimmer above the iceberg, produced by light diffraction by fog or at night time when moonlight falls on the opposite side of the iceberg.

ICEBERG MELTING AND DESTRUCTION INTENSITY. The rate of iceberg melting expressed in units of length. Melting and destructive processes are different in the different regions where icebergs are formed and drift. For instance, in Baffin Bay the height of the above-water part of icebergs decreases 0.7 meter every day, whereas in Davis Strait the height of an iceberg may decrease by 1.3 m/d. Near Newfoundland typical values are 2.0 m/d while further to the South near the Grand Banks values as high as 3.3 m/d have been observed. The rate of decrease in the height of icebergs is determined by the fact that in the above regions the summer air temperature considerably exceeds the summer water temperatures. In some cases, when an iceberg enters warm waters melting and destruction accelerate rapidly because of the increase in water temperature. It is a well known fact that a large iceberg (with a length of 127 meters) that entered the Gulf Stream melted away within 36 hours.

In the case of icebergs located in the Antarctic, the decrease in the heights of icebergs caused by the melting of their upper surface is 2 - 3 meters per year.

ICEBERG RAMS. An underwater portion of an iceberg that protrudes for long distances (in extreme cases 300 - 500 meters) beyond the visible (above water) sides of the iceberg. Iceberg rams and iceberg fragments with low free-boards cannot be detected by radar and are therefore very dangerous for shipping.

ICEBERG SEASONS. Periods of iceberg development and spreading during an annual cycle, particularly relative to established shipping lanes. For example, the minimum quantity of icebergs in the North Atlantic is observed in November-January, while the maximum quantity (80% of the total annual iceberg quantity) occurs from April to June.

ICEBERG STUB. An accumulation of pieces and fragments of icebergs located to the windward behind a large iceberg and with a small deviation either to the left or to the right depending upon the hemisphere. A stub may only appear on the lee side of an iceberg when there has been a rapid change in the wind direction.

ICEBERG TONGUE. A large accumulation of grounded icebergs starting from the glacier barrier and stretching into the sea for a long distance (sometimes up to 120 km). Iceberg tongues are only found in the Antarctic Regions.

ICEBERG WATERS. Waters where one can expect to meet at least one iceberg.

ICE BERTH. A natural wall of a glacier, ice cliff, or an artificial frozen ice mass on the shore used for mooring vessels so that they can be loaded or unloaded at locations not normally equipped for such activities.

ICE BLINK (ICY SKY). A glimmering shine at the lower edge of clouds caused by light reflected upward from an ice surface. It is a clear indication that ice is close.

ICE BLISTERING. The volume of isolated gas (usually air) bubbles, expressed as a percentage of the total ice volume.

ICE BOUNDARY. A line on a map indicating the boundary between drift ice and open water (actually this is commonly a transition zone).

BOUNDARY OF MAXIMUM ICE EXTENT. The line that designates the part of a sea beyond which ice has not been observed during the available series of observations. It serves to indicate the area where the probability of ice is 0.

BOUNDARY OF MINIMUM ICE EXTENT. The line that designates the part of sea where ice has always been observed within the entire period of observations. It serves to indicate an area where the probability of ice is 1.

ICEBREAKER. Commonly a specially designed vessel which performs ice breaking on shipping routes that cross ice covered waters ( Photograph 35). Their hulls are designed to utilize the most effective mechanical method for inducing ice sheet failure; breaking the ice by using the weight of the icebreaker to create a bending moment in the ice sheet.

ICEBREAKER PILOTAGE OF VESSELS. The navigation of a convoy piloted by one or more icebreakers.

ICEBREAKER PILOTAGE OF VESSELS BY TOWING. A pilotage technique when vessels are towed along the channel by an icebreaker ( photograph 36). The number of vessels in a convoy is usually restricted to a single vessel and a single icebreaker. In practice, however, one icebreaker may tow two or more vessels. It is also possible for one vessel to be towed by two icebreakers.

ICEBREAKER PILOTAGE OF VESSELS BY LEADING. A pilotage technique when a convoy consisting of one or several vessels follows one icebreaker (simple convoy), or when a group of vessels follows several icebreakers (complex convoy).

ICE BREAKING AREA. An area of coastal and shelf glaciers containing large numbers of cracks and crevasses and where the calving of icebergs is occurring ( Photograph 37).

ICE CANOPY. The lower underwater surface of an ice cover as observed from below. This expression has been primarily used by the submarine community.

ICE CLASSIFICATION. A notation system establishing different classes of ice typically presented in the form of tables (charts) and used to establish links between these concepts or classes. An ice classification facilitates work when a large number of ice related ideas and ice types are under study. Ice classifications take into account existing logical links between different ice types with a view of determining the place of each ice type in a general system. This place is usually connected with the origin of the properties of the corresponding type of ice.

As an example, consider the structural-genetic system of ice classification in natural water bodies proposed by N. V. Cherepanov. In this system, ice is subdivided into three groups according to its crystallographic characteristics. In turn, each group includes 9 types of ice. Classification of ice under this system clearly shows that there is a connection between hydrometeorological conditions and the crystal structure of the ice ( Figure 3). In Figure 2 only the groups representing fresh water and sea ice are shown as Cherepanov felt that there was, as yet, insufficient data to adequately classify brackish ice.

ICE CODE. A system of symbols for communication, processing and storage of ice related information. The symbols may be in the form of numbers or characters.

ICE COMPRESSIBILITY (VOLUME ELASTICITY MODULUS). The reversible change of ice volume V under the effect of hydrostatic pressure P that, in the case of an ice volume decrease, is controlled by the elastic repulsion of atoms. Compressibility is an important characteristic when considering the behavior of ice under high pressure.

Quantitatively compression is described by the modulus of volume compression:

,

or by the compressibility coefficient:

.

One can also distinguish between isothermal (when T = constant) and adiabatic (when entropy S = const) compressibility. Adiabatic compressibility is connected with isothermal compressibility through a relation containing the thermal capacities at constant pressure CP and volume CV:

The difference KS – KT is proportional to T and is small at typical temperatures.

ICE CONCRETE. A frozen mix of water, sand, gravel or wooden material, characterized by a high mechanical strength.

ICE CONDITIONS. A combination of parameters and indicators selected from the general number of ice sheet characteristics which have been found to be useful in assessing the degree of the impact of the ice on the course of a naval operation or any other activity.

ICE CORES. Cylindrical samples of ice obtained by means of specialized coring devices. Such cores as frequently used for studying ice structure and the physical properties of ice.

ICE COVER. The expression ice cover typically refers to the total ensemble of ice types covering a body of water. Commonly an ice cover is heterogeneous consisting of areas of ice that differ in ice thickness, horizontal dimensions, surface relief, age and concentration.

ICE COVER DYNAMICS. Various forms of ice sheet motion which, under the influence of external forces, can result in changes in the structure, state and distribution of the ice.

ICE CREEP. Continuous plastic deformation of ice subjected to a constant stress.

For ice monocrystals creep is controlled by the slippage over one another of molecular layers oriented parallel to the basal planes. Because of defects, creep rate at a given stress is invariably larger than values forecast from theory.

The change in shape of an ice sample during deformation and the numerical value of the creep deformation of a monocrystal depends significantly on the direction of the load in relation to the direction of the C-axis of the crystal. For example, in accordance with data obtained by A. Higashi, the minimum stresses that cause creep in directions parallel to the basal planes were 0.4 MPa, while for creep perpendicular to the basal planes values were 9.0 MPa - an increase of 20 times.

ICE CREEP CURVE. The dependence of ice strain e vs. time t under constant stress (s = const). The stress–strain state of the ice can be described by means of a set of creep curves.

The changes in the creep curve with time depends on a number of parameters (such as temperature, ice structure, direction of applied load, etc.). The deformation of polycrystalline ice, which can be considered a ductile solid, follows certain laws. After the initial elastic deformation, which develops essentially instantaneously (OA in Figure 7), the creep deformation begins. Creep can be divided into three stages. For instance, at s = s AB is the stage of transient creep with a decreasing creep rate(0<t<t1). This stage is also called a stage of primary or decreasing creep. BC is the stage of steady-state creep with a virtually constant deformation rate (t1<t<t2). It is also called secondary creep. If the temperature and load are sufficiently low, secondary creep may last for a long time. This stage (of a slow transient process) is characterized by the existence of inflection point M, whose tangent line gives the rate of a secondary creep. CD is tertiary or accelerating creep, a progressive process which is characterized by accelerating deformation leading to the rupture of ice (t2<t<ts2). The transition to the tertiary process occurs as a result of the ice crystals starting to undergo a process of recrystallization.

At strains which do not exceed a certain critical value (called by K. F. Voitkovskii the limit of long-term creep), the deformation shall continuously increase at a constant rate. The value is characterized by the fact that if s > the ice creep is accompanied by a formation of microcracks, which leads to an increase in the ice volume and a decrease in its density.

As the stress increases, the duration of secondary creep diminishes and nearly disappears. Further stress increase over the ultimate strength value results in the brittle breakage of ice. Experimentally obtained creep curves can be used to determine the rheologic parameters of ice which can then be used to determine a phenomenological equation of state for various conditions of deformation.

ICE CRUST. A layer of solid ice on the surface of the snow cover or the land.

ICE CRYSTALS. The principal form of existence of the solid phase of water under natural conditions. Formed as a result of either forced or spontaneous crystallization, ice crystals have a hexagonal crystal lattice and belong to the ditrigonal-pyramidal symmetry group of the trigonal system.

A variety of different types of ice crystals occur naturally. For instance, one can distinguish one-dimensional crystals - needles (crystals that grow in the direction of the C-axis); two-dimensional crystals - lamellar crystals (crystals that grow along the direction of the basal planes); and three-dimensional crystals - grains (isometric crystals that grow equally in all three dimensions).

ICE CRYSTAL TRANSLATION PLANES. Surfaces that divide the basal planes of ice crystal ( Figure 1).

ICE DEFORMATION. A change in the shape and dimensions of an ice crystal or of a compact ice body or its elements caused by external mechanical forces or by thermal changes.

ABSOLUTE ICE DEFORMATION (ABSOLUTE ICE ELONGATION). The deformation of ice expressed in units of length.

BENDING (FLEXURAL) ICE DEFORMATION. A complicated form of ice deformation (samples are usually in the form of plates or beams) where the upper and the lower layers of ice, depending on the direction of the bending force, are subjected to different types of deformation: i.e., of compression or elongation. Bending deformation is also distinguished by the presence of a so-called neutral plane which is not subject to deformation (i.e., its dimensions do not change) during the flexing.

ELASTIC ICE DEFORMATION. Deformation of ice which is characterized by reversible changes in dimensions and shape, i.e., the changes disappear after the removal of the deforming forces.

ELONGATION DEFORMATION OF ICE. The most simple type of deformation characterized by the elongation of the ice along the direction of a stretching (tensile) force exerted on the elements constituting an ice body .

PLASTIC (RESIDUAL OR INELASTIC) ICE DEFORMATION. Deformation of ice resulting in irreversible changes in the dimensions or shape of the deformed body, i.e. permanent changes remain after the removal of the deforming force.

RELATIVE DEFORMATION (RELATIVE ELONGATION). Deformation expressed using relative units (e.g. in percent), and defined as the ratio of the absolute deformation to the initial dimensions of a body element being measured.

In the case of simple elongation of ice elements, the relative deformation is defined by the equation:

,

where is the length of the ice element in question after the deformation and is the length of the same element prior to deformation.

In the general case, deformation is described by three parameters:

where u, v, and w are components of the displacement vector.

SHEAR DEFORMATION OF ICE. An deceptively simple appearing type of deformation which is characterized by changes in the angles of elementary parallelepipeds of a deformed body while maintaining constant dimensions of the different faces. Shear deformation is caused by tangential stress t ( Figure 8). As a result, the rectangular parallelepiped abcd is transformed into the oblique parallelepiped ab1c1d of the same volume. Translation b1b is called an absolute shift of face bc with respect to face ad; the angle g is called a shear angle; and tan g - a relative shift. In actuality, such shifts usually induce complex stresses within the deforming body namely tension, compression and bending. In such cases, tangential stresses are accompanied by normal stresses.

UNIAXIAL COMPRESSION OF ICE. The deformation characterized by a change in the linear dimensions of a cylindrically or prismatically shaped compressed object along the direction of the applied compressing force.

VOLUME ICE EXPANSION. A general volume deformation which can be considered to be a combination of relative deformations along three orthogonal axes. The change in volume is described by the following formula:

.

The relative volume expansion has a corresponding mean relative elongation:

ICE DEFORMATION TENSOR. A compact method for mathematically representing the deformation of an infinitely small parallelepiped specified as existing near a particular point in the ice. The deformation is represented by a symmetric tensor of the 2nd order.

The deformed state of an ice element can be considered to be known if the components of the ice deformation tensor are known.

ICE DENSITY. The mass of a unit volume of ice. The density of air-free clear ice at a temperature of 0°C, and a pressure of 1.01 105 Pa is equal to 916.7 kg/m3. Accordingly the specific volume is 1.0908 cm3/g.

ICE DIFFUSION. A motion of an ensemble of ice-floes resulting in a decrease in the compactness of the ice. Such diffusion occurs under the influence of turbulent fluctuations in the drift velocity caused by eddies in the underlying layer of water and by mesoscale pulsations in the wind velocity. Ice diffusion results in the statistical smoothing of ice cover characteristics and the displacement of the edge of the ice pack into areas that were formerly ice free.

ICE DRIFT. A translational motion of ice occurring under the influence of external forces. For instance, the direction and velocity of ice drift are affected by both the wind and currents as well as by the Coriolus force (a apparent deviating force resulting from the rotation of the Earth), the seafloor relief, and the nearness of the coast.

DIRECTION OF ICE DRIFT. The angle between an ice-floe drift vector and true north.

VELOCITY OF ICE DRIFT. A quantitative descriptor of ice-floe motion. The velocity is determined as the ratio of the displacement vector to the period of time during which this displacement occurs.

ICE ECHOGRAM. The profile of the lower surface of the ice as determined by an upward-looking sonar system operated on a bathyscape or submarine moving under the ice sheet ( Figure 9).

ICE EDGE. The boundary between open water and sea ice of some specified degree of compactness. If the boundary is tightly defined, it is referred to as a compact ice edge ( Photograph 24). If the boundary is poorly defined, it is called a diffuse ice edge ( Photograph 38).

ICE ELASTICITY. The property of ice that characterizes its ability to resist the change of volume and shape resulting from mechanical stresses that occur in the ice due to external loads, volume forces, temperature gradients, and other sources of stress provided Hooke’s Law is observed (i.e. that the strain is a linear function of stress).

ICE EXCLUSION. See desalting of sea ice.

ICE-FILM. A frozen snow crust on the surface of the ice. Ice-films should be distinguished in accordance with their origin. wind, sun, and thaw process.

ICE-FLOES DRIFT. The movement of ice-floes in relation to each other that may be followed by the formation of an open water spaces between them or by the development of strips of brash ice at locations where the floes are in contact.

The measuring units of ice drift are: the displacement vector, the angle of rotation of the ice floes in relation to each other, and the speed of these movements.

ICE FORECAST. A scientific forecast of the onset and duration of various stages (phases) of an ice regime. Items specified include the spatial distribution of the ice as a function of time as well as qualitative estimates of changes in its state and structure.

ICE FORECASTING METHODS. A combination of methods and techniques for establishing casual relationships between forecast phenomenon (process) and other essential factors.

PHYSICO-STATISTICAL METHODS. A method for preparing ice forecasts based on the analysis of factors which are responsible for a given phenomenon (process). The method includes an accurate analysis of the initial state of the ice sheet and employs hypothetical models of different ice processes.

Physico-statistical methods of ice forecasting are based on the intensive use of data obtained by spectral, correlation, and regression techniques as well as by other methods of statistical analysis.

Climatic method. A method of ice forecasting based on the high reproducibility of multi-year average values of ice regime parameters.

The climatic method is used in cases when the distribution of an analyzed parameter is close to normal.

Method of analogy. A method of ice forecasting based on the utilization of anomalies of the principal predictor for a several year period. The anomalies are then compared with the average values of the forecast phenomenon, process or ice regime element for the same year. This approach may be used to construct tentative ice forecasts.

Method of basic models. A method of ice forecasting based on the use of a set of standard situations which took place in the past. The standard situations are then used for predicting comparable future situations compatible with some distribution of the predictor.

Method of inertia. A method of ice forecasting based on the tendency for ice processes to maintain their intensity, direction and existing state for a certain period of time. The degree of persistence of ice processes can be evaluated with the help of the autocorrelation function that characterizes the relation between parameter values of an ice regime as a function of time.

Method based on typical ice conditions. A method of ice forecasting based on the classification of ice phenomena or ice processes according to properties which serve as a determining criteria for each ice type. Each type is then characterized by a set of average values for parameters and indicators that pertain to the particular ice regime or ice cover of interest.

This method is widely used in the preparation of qualitative long-term forecasts that predict the distribution of ice and other elements of an ice regime.

Numerical methods. Methods of ice forecasting that are based on the use of mathematical models describing the evolution of an area of ice. Such models commonly include sets of differential equations describing the mass and heat balance and the momentum and salt concentration. These sets of equations are then solved numerically.

ICE FORMATION.

(1) The process of forming a primary ice layer over the surface of a water body.

Ice formation is now typically noted in terms of two dates: the date of the initial ice formation (when the first ice was observed on the water surface regardless of its amount) and the date of the initiation of a steady ice formation process (beginning from this date, the process of ice formation acquires a steady character despite possible interruptions).

If the primary ice disappears due to a sudden rise of temperature, the interruption may last up to two days.

If the primary ice is driven away by a wind, but if the temperature of the water surface does not exceed the temperature of freezing, then the interruption may last up to three days.

For ice formation to occur, two conditions must be met: the supercooling of water and the intense removal of heat to the atmosphere.

(2) A solid body formed by sea or fresh water ice floating on the surface of the sea.

FLOE OF CONGLOMERATED ICE. A floe that consists of ice of different ages and sizes frozen together ( Photograph 39). At present, three types of conglomerated ice fields can be distinguished.

ICE DISK (PANCAKE). A floe of an oval, nearly circular shape, with a ridge of snow ice along its outer edge (Photographs 4 and 39).

ICE PLATE. A plane piece of a primary compact ice layer or black ice outlined by narrow strip of rafted ice. The predominant shape of an ice plate in an ice sheet is rectangular.

Floe of multi-year conglomerated ice. A floe consisting of conglomerated multiyear ice which forms a monolithic rounded block on the surface of which one can see smoothed hummocks and hummock ridges. A field of multiyear conglomerated ice is usually surrounded by first-year thick ice containing large hummock ridges. The diameters of fields of multiyear conglomerated ice range from 600 to 800 meters.

Floe of autumn conglomerated ice. A floe consisting of multiyear ice frozen together by first-year thick ice. The border of an autumn field of conglomerated ice is formed by young ice. The average diameter of an autumn field of conglomerated ice is 2 - 3 kilometers.

Floe of unstable conglomerated ice. A gigantic or very large ice field which includes fields of multiyear and autumn ice frozen together by thin first-year ice. A field of unstable conglomerated ice is limited by leads in which there is black or young ice. The diameter of unstable conglomerated ice fields may range from 8 to 12 kilometers.

BLOCK OF ICE. A part of an ice field consisting of uniform ice limited on all sides by cracks and leads or on two sides by cracks or leads and on the other two sides by hummock ridges. A block of ice usually has the form of a parallelepiped with angles equal to 70 and 110°.

ICE FIELD. The largest formation of drifting ice.

Small ice floe. An ice floe with a width of 20 – 100 m. This term was used before 1974.

Medium ice floe. An ice floe with a width of 0.1 – 0.5 km.

Big ice floe. An ice floe with a width of 0.5 - 2 km ( Photograph 7).

Vast ice floe. An ice floe with a width of 2 – 10 km.

Giant ice floe. An ice floe with a width exceeding 10 km.

FRAGMENT OF AN ICE FLOE. A part of an ice floe with a width of 100 - 500 m formed as a result of fragmentation of the floe.

PATCH FLOE. A part of an ice floe fragment with a width of 25 - 100 meters formed as a result of further fragmentation of the ice floe. An agglomeration of patch floes is called fragmental patch ice.

FRAGMENTAL FLOE. A fragment of a large-sized floe with a width of 20 to 25 meters. An agglomeration of such floes is called fragmented ice.

Floe with ram. A fragment of a floe with an under-water ram which is formed as a result of non-uniform melting of its sides and the erosion of the above-water part of the floe.

Mushroom-shaped floe. A fragmental floe formed as a result of the fast melting of ice in its middle section and the formation of a base (stem) supporting the ice overhang.

Floeberg. A fragmental floe formed from a large-sized hummock or a group of hummocks after the ice surrounding it has melted. Floebergs can be very large, impressive features ( Photograph 40).

BROKEN ICE (BRASH). Fragments of ice formed as a result of grinding caused by the compression ( Photograph 27). The diameter of each fragment does not exceed 2 meters.

PIECE OF ICE. A split part of a floe with a diameter up to 10 meters.

ICE FRAGMENTATION (CATACLASIS). Ice is particularly susceptible to this form of dynamic-metamorphism because of its brittle nature. Cataclasis is characterized by extreme cracking, fragmentation and granulation of ice sheets under the effect of thermo-physical and dynamic processes.

ICE-FREE NAVIGATION. A period between the date in the spring when a route becomes free of ice and the date in autumn when new ice starts forming.

ICE-GOING CAPACITY. The ability of a vessel to navigate in ice at a given velocity.

ICE-GOING PROPERTY OF VESSEL. A combination of specific vessel properties determined by the shape and strength of the hull, the capacity of the power plant, and the presence of special schemes and facilities designed for increasing the vessel operation efficiency in ice.

ICE GRAIN. An irregularly edged ice crystal.

ICE GROWTH. The process of ice formation and thickening that results from the fact that during the winter in the polar regions the amount of heat lost to the atmosphere from both open water and the surfaces of ice sheets exceeds the heat transferred from the water to the bottom of the ice. The result once the water layer in contact with the ice has cooled to the freezing point is the freezing of a thin water layer whose release of heat is exactly equal to the excess amount of cooling.

An external feature of this process is the time attributed to the age stages of an ice sheet development that is fixed by the following dates: the dates when the ice reaches a thickness of 1-10 cm (the day when new ice is observed on the water surface); the dates when young ice 10 to 30 cm thick is observed (the day when gray and white ice appear on the surface of the sea); the dates when the ice reaches a thickness of 30, 50, 70 and 120 cm (the days when the different stages of first year ice initially occur (i.e. first stage thin FY ice, second stage thin FY ice, medium FY ice and thick FY ice); and finally the date the ice-thickness at a given point of observation reaches its maximum value during the current year.

ICE HARDNESS. The capacity of ice to resist the penetration of another body usually in the form of an indentor which receives no residual deformation and has a spherical or pyramidal shape. Hardness is defined as the ratio of the effective load P to the surface of the resulting dent S. Therefore the hardness H = P/S can be considered to be the average value of pressure in the dent. Depending on the ice temperature and the length of time of load application (dynamic hardness corresponds to short times and static hardness to long times), the H value may differ by more than one order of magnitude.

ICE HEAP. A conglomeration of ice-floes on the shore of a water body.

ICE HILL. A monolithic rise on the surface of multiyear ice formed as a result of multiple melting and refreezing events which round the surfaces ( Photograph 9) and cement the ice blocks in preexisting large hummocks into a monolithic mass ( Photograph 41). Ice hills up to 90 centimeters high do not necessarily require the presence of preexisting hummocks and can develop as the result of non-uniform melting of initially flat (undeformed) sea ice.

ICE IDIOMORPHISM. A tendency of ice to take on crystallographic shapes when solidification occurs from either water or water vapor. The crystal shapes mirror the geometry of the ice I(h) structure: e.g. the ice may have the shape of hexagonal stars, prisms, pyramids, etc.

ICE KEEL. A crest in the under-water part of a hummock ridge.

ICE LAYER. The ice between two surfaces of a divide or a sheet of ice characterized by a homogeneous structure.

ICE LOAD. See Ice pressure.

ICE MANEUVERABILITY. The ability of a vessel to make turns, keep on course, run into ice edges when advancing or running astern, move parallel to the edge of a channel, and accelerate under a variety of ice conditions.

ICE MARKER. A closed tube containing a copy of an ice map showing the recommended navigation route. The ice marker is dropped from an aircraft or helicopter onto the cargo vessel or an icebreaker navigating in ice. The tube is usually of red color and has a rope not less than 20 meters long with a small red flag fastened to its end. This is an obsolete term as this method of transmitting ice maps is no longer in use.

ICE MASSIF. A significant region of an ocean or a sea that contains heavy, compact pack ice during all seasons of the year. Ice massifs typically having a compactness of over 7 points and an area of more than 1 thousand km2.

OCEANIC ICE MASSIF. The ice massif of the Arctic Ocean that in the winter completely covers the water area of the Arctic basin and most arctic seas, and has the horizontal dimensions of between 1,950 to 2,300 km. Depending on the morphometric features of the ice forming it, two independent subtypes may be distinguished: the Siberian suboceanic ice massifs and the Canadian suboceanic ice massifs.

REGIONAL ICE MASSIFS. Stable accumulations of uniform and consolidated ice occupying whole seas or large parts of them. The areas of these ice massifs are subject to seasonal and interannual changes. In recent years, such massifs were given a new name: "spur" ice massifs as long as they spread into marginal arctic seas in the form of spurs of oceanic massifs of old ice.

LOCAL ICE MASSIFS. Sufficiently stable accumulations of ice having a compactness of 7 to 10 points and covering the separate regions or parts of an ocean or sea. Their changes in area has a seasonal character: at the beginning of summer they become isolated and the extent of their existence depends on the hydrometeorological conditions of a specific summer period.

LOCALIZED ICE MASSIFS. The temporary accumulation of compact, very compact, and consolidated ice formed as a result of the separation of a part of a local ice massif during the summer melt period. The time of their occurrence and their coverage area depends on the intensity of thermodynamic processes proceeding over a given region of the sea in the summer. The horizontal dimensions of such massifs change from 35 to 85 km. An illustration of this may be found in the southern part of the Taimyr ice massif which is occasionally isolated in the southwestern part of Laptev Sea.

ICE BELT. An accumulation of compact drift ice some tens of kilometers wide and hundreds of kilometers long. An ice belt usually follows the coast line or occurs on the edge of a regional massif.

ICE ZONE. A part of an ice sheet in the form of an unstable ice accumulation that differs from the ice sheet that surrounds it by its structure, state, relief, and dynamics. Although the configuration of an ice zone and its area may be different, they vary from 9 to 35 km across. At the present, zones of rasvodije (clear water areas), broken ice, rarefied ice, compact ice, and compressed ice are distinguished.

ICE SPOT. A temporary accumulation of ice that differs from the ice sheets surrounding it by some particular feature such as compactness (uniformity). Horizontal dimensions of a spot vary from 0.5 to 9 km.

ICE STRIPS. Narrow (not more than one kilometer wide), collinear accumulations of drift ice that are usually observed near the edge of a region of pack ice.

ICE TONGUE. An accumulation of ice-floes stretching in the direction of open water or a zone of rarefied ice in the form of a narrow short spur.

ICE DAM. The contact zone of two compressed ice fields or accumulations of compact ice in the form of a narrow ice area that is difficult to navigate even by ice-breakers.

ICE MASSIF PERIPHERY. A solid or broken zone of ice showing a decreased compactness as compared with the ice massif that it borders on one or more sides. Widths will vary depending on the season and the intensity of the destructive processes that are operating in the off-edge regions of the massif.

ICE MECHANICS. A technical science adjacent to glaciology, ice science and ice thermodynamics. The subject of ice mechanics is concerned with problems such as the physical-mechanical properties of the various structural-genetic types of natural ice, the strength of natural ice sheets as they exist in nature, the varied interactions between ice sheets and hydrotechnical structures and vessel hulls, and the development and application of various methods to minimize the negative effects of ice phenomena.

ICE MELTING. The process of ice transferring from the solid to the liquid state. Melting in an ice mass invariably results in a decrease in its strength, thickness and horizontal dimensions, ending in its complete disappearance. Under natural conditions, ice melting occurs from the upper and lower surfaces as well as from the sides.

The initiation of sequential stages of this destructive process is fixed by the following dates: the date of first melting (the day when the air temperature reaches the melting temperature for a given salinity); the date of the first occurrence of puddles (snezhnitza, Russ.) (i.e., the day that dark spots of wet snow appear on the snow-covered surface of the ice sheet); and the date when small ponds occur (the day when small bodies of thawed water begin to develop on the ice sheet surface) [Each age of ice has an associated pattern of small ponds and open water areas.]; the date when thaw holes and patches occur (the day when round-shaped melted holes and patches that completely penetrate the ice appear); and finally the date of off-shore water occurrence (the day when a strip of water forms due to the melting of snow on the ice or the flow of water onto the ice from the shore).

ICE MELTING TEMPERATURE. The temperature at which ice melting occurs at some constant external pressure. Sea ice melting does not occur at a fixed temperature (as with pure ice), but continuously over a temperature range, starting when the temperature is still appreciably below 0°C.

ICE MONITORING POST. An area of a water body where visual and instrumental monitoring of ice conditions is carried out.

ICE MORPHOMETRY. The section of geomorphology which studies methods for defining and the meanings of the varied geometric shapes and dimensions of relief forms that develop on the upper and lower surfaces of ice sheets.

ICE NAVIGATION. a) The navigation of vessels when ice is present on a given route. b) A navigation period of a cargo vessel in ice.

ICE OPPOSITION. The phenomenon of regular antagonistic changes in the state of the ice sheets in two different geographic regions.

ICE OVERHANG. Ice overhangs characteristically form at the edges of floes which is the result of melting and thermal erosion ( Figure 10). Overhang widths measured toward the floe edge may be as large as 1 meter. Such features have a low load-bearing capacity and can be quite hazardous to individuals working near floe edges.

ICE OVERLAP. A part of an ice-floe or its fragment located on the edge of another ice-floe as the result of compression between adjacent floes.

ICE PHENOMENON. Registered ice-related events that represent stages of various ice processes.

ICE PLASTICITY. The property of ice to irreversibly become deformed under the effect of external forces or due to the occurrence of internal stress.

The measure of irreversible changes in the interdisposition of particles in a material is the plastic distortion tensor which is the symmetric part of the plastic deformation tensor . The components of this tensor [provided that elastic deformation is small compared to the plastic deformation (i.e., that )] are not simply connected with the components of stress tensor s. As long as is not a function of state, there are no ice plasticity characteristics connecting and s that could be considered as constants similar to the elasticity constants that connect the elastic deformation tensor and s.

The speed of plastic deformation depends on instantaneous s values, temperature T, and the ice structure. When there is a linear connection due to the availability of non-equilibrium ice structure defects (e.g. dislocations), the plastic deformation is called quasi-viscous ice flow.

ICE PLATFORM. An artificially created ice slab (platform) on the surface of the water or land used for loading-unloading operations, the drilling of wells, and research studies. An ice platform is made by consecutively freezing layers of water on the platform surface with the possible additions of snow, pieces of ice, and reinforcing materials.

ICE POLLUTION. The process of accumulating various undesirable foreign substances in an ice volume or on its ice surface.

ANTHROPOGENIC POLLUTION. The direct or indirect influence of human activity on the natural pollution intensity of an ice sheet.

MECHANICAL POLLUTION. The polluting of an ice sheet by agents that have only an effect on its mechanical properties (e.g., rubbish or other materials characterized by a slow rate of degradation resulting from physico-mechanical or biological processes) ( Photograph 42).

NATURAL POLLUTION. The polluting of an ice sheet as a result of natural processes: sand storms, volcanic eruptions, etc. (see also Photograph 42)

ICE POROSITY. The dimensionless ratio of the volume of pore space in an ice sample relative to the total volume of the sample. Sometimes, ice porosity is expressed as the value of its pore volume per unit mass of ice. In this case, the dimensions of porosity will be [cm3/kg]. The porosity of compact clear ice does not usually exceed 1 cm3/kg. The porosity of strong sea ice is usually equal to 1-50 cm3/kg. Turbid ice may show porosities in the range of 10-100 cm3/kg. Ice types, which have porosities ranging from 50 to 400 cm3/kg are similar to snow.

ICE PRESSURE. A scalar value which characterizes the stressed state of a continuous medium. If the medium is in equilibrium, the pressure is equal to the negative normal stress applied to an arbitrarily oriented element at a given point. In cases when the ice is considered as a medium with internal friction, the pressure P (taken with a negative sign) is defined as the average arithmetic value of the three normal stresses at a given point and is also presented as a scalar equal to one third of the linear invariant of the stress tensor.

Depending on the orthogonal system of coordinates,

In the mechanics of a continuous media this sum is called the mean or hydrostatic pressure.

In the technical literature, the term ice pressure is usually used to denote the force with which an ice sheet affects the shore, vessels, or any hydrotechnical structure that it contacts. Ice motion against a structure results in the occurrence of dynamic pressure, while thermal expansion gives rise to static pressure. In these cases ice pressure is often expressed in units of force per meter of the horizontal contact with the structure.

ICE PROCESSES. Processes causing changes in the initial state of an ice sheet, as described either by the conditions that have led to that particular state, or by interactions between an ice sheet and the surrounding media resulting in changes in either.

ICE RAM. An underwater ice protuberance on a side surface of an ice-floe, iceberg or ice barrier, formed as a result of more intensive ablation in both the above-water part of the ice and in the wave-cut zone.

ICE RAREFACTION. The process by which the distances between ice-floes are increased as the result of either thermal and dynamic factors.

ICE REGIME. A stable sequence of events describing the initiation and evolution of natural ice phenomena and their associated processes. A description of an ice regime stresses the regular nature of the temporal changes in a variety of spatial parameters characterizing the ice as caused by a combined influence of the local climate and the dynamics and geometry of the associated water body.

ICE RELAXATION. A term describing the process of ice, that has been disturbed in some way, returning to a state of thermo-dynamic equilibrium. In a closed macroscopic system such processes are irreversible because of dissipative losses of energy.

ICE RIND. See glass ice.

ICE ROAD. A part of an ice sheet that can be used as a roadway for transport vehicles [e.g., "ice road of life" across Lake Ladoga that connected Leningrad during the World War II blockade and the "Big Earth"(unoccupied territory of the USSR)].

ICE ROUGHNESS. The aggregate unevenness on either or both upper or lower surfaces of a floating ice sheet ( Photograph 43). Roughness is commonly characterized by the deviation of the actual surface profile from an average profile line of a given length. Variations in the roughness affects the strength of the coupling between the ice and the wind and currents.

ICE RUNNING VELOCITY OF A VESSEL. The maximum navigation velocity at which a vessel can move through large areas (over 1.5 - 2.0 km) of uniform ice while still navigating autonomously.

ICE SEASON. The period of time during which a given water body retains its ice sheet.

ICE SHEET. An ice sheet is a continuous, homogeneous, relatively level component of an ice cover.

ICE SHEET STABILITY. The ability of the ice sheet to preserve its spatial structure and features in time.

ICE SKY. See ice blink.

ICE-SLICK. Fresh-water ice of atmospheric origin occurring on the surface of objects. It commonly develops due to the freezing of melted snow.

ICE SPIRALS (EDDIES). A spiral-shaped distribution (eddy) of more compact ice in a region of open ice or in the vicinity of an ice edge. Diameters of ice spirals vary approximately from 1 to 200 kilometers.

ICE SPLITTING. A method of combating the build-up of ice on ships or offshore structures by mechanically separating the ice from the structure and then discarding the fragments. One common procedure involves the use of wooden or rubber mallets.

ICE STATE. Characteristics of the ice sheet in a given part of the sea or along a shipping route as recorded on photographs, radar, TV, etc. or depicted on an ice map with the help of a set of conventional symbols. By describing ice conditions one can assess the momentary state of a region of sea or lake ice.

ICE STRATIFICATION. Horizontal layers of different structural, compositional and genetic types of ice occurring in an ice sheet.

Ice stratification is usually produced by changes in the hydrometeorological conditions during the period of ice formation, growth, and destruction. For instance, sharp changes in growth rate can result in changes in the amount of brine and gas trapped in sea ice resulting in a visual layering ( Photograph 18). It is also possible to distinguish a seasonal ice stratification which separates the ice into annual layers as the result of thermometamorphic processes. One of the most striking causes of stratification is rafting in thin ice which can result in numerous, essentially identical layers.

ICE STRENGTH. The property of ice that enables it to react to different mechanical loads and to the non-uniform influences of a variety of physical fields without undergoing failure. The process of ice failure, as with any other material, depends on many factors that are not always well known.

The strengths of different types of ice depend, to a great extent, on the arrangement of the structural elements in the particular ice type. Strength is also significantly affected by external conditions: the types and rates of loading, the thermal regime, the roughness of the surface of the samples, etc. Real ice contains multiple flaws varying from submicroscopic and microscopic defects to large pores and voids and major cracks. As a result, the strength of ice is invariably a function of sample size.

The problem of strength is currently considered from two different viewpoints: mechanical and kinetic. According to the mechanical concept, failure is the result of the loss of stability by a solid body. It is assumed that each material is characterized by a certain threshold value of the stress that it can sustain. When the stress is below that threshold, the body is stable and can retain its integrity under load for an indefinitely long time. This threshold stress is a measure of the strength of the body.

An important aspect of the kinetic concept of strength is the development of failure, which occurs gradually as a consequence of the development and accumulation of submicroscopic cracks. This process also occurs in bodies stressed as the result of thermal fluctuations. The idea of the lifetime under load is significant, i.e. the time required for the development of the process from the moment the load is applied to the time of failure. It is impossible to give a comprehensive answer to the question of what load a body can endure, i.e. what is its strength, without specifying the time the body is required to remain intact. This implies that the terms ‘ultimate strength’ and ‘ultimate rupture stress’ are relative. Although they make little sense in terms of the physical nature of the strength of solid bodies, they are quite convenient in practice.

ICE STRENGTH CURVE UNDER BIAXIAL COMPRESSION. The dependence of the ultimate failure strength of an ice sample which is subject not only to an axial compression, but also experiences lateral compression or stretching.

In accordance with theoretical failure mechanics, the transition from the strength characteristics applicable in the case of uniaxial loading to the description of the strength under conditions of combined stresses (e.g. biaxial compression) is made by introducing experimental criteria (strength criteria, strength theory, strength hypotheses) which describe the data on a complex stressed state.

Ice belongs to a family of materials which behave differently under compression and tension. The compressive strength of ice exceeds its tensile strength by a factor of 3 to 5. When ice is subjected to biaxial compression, one can use the so-called Mohr criterion. This criterion can be formulated as follows: if we assume that the tangential stress on the "failure area" depends on the normal pressure acting on this area, i.e., , then on the plane this function will be presented by a curve delimiting the area of safe states.

Assuming that the above dependence can be approximated with the help of the Coulomb relation

tn = F + sn tan j

and using the experimental dependence ( Figure 11), represented by an envelope of Mohr circles (e.g. constructed with the help of principal stresses measured for a nonuniform triaxial compression at s ¹ s2 = s3 > 0, i.e. for an uniaxial compression in the presence of lateral or radial pressure in the case of a cylindrical sample), one can determine the angle of internal friction , which determines the ability of ice to exhibit plasticity under stresses which exceed its elasticity limit. One can also calculate the cohesion of ice F, a parameter which characterizes the volume strength of ice. Parameters and F are not constant. As the stress grows, the value of increases and ultimately tends to the maximum value of the tangential stress (at j ® 45°).

It has been shown that the axial strength of anisotropic sea ice, tested in directions that are parallel and perpendicular to the crystal alignment may differ by more than a factor of 1.5, provided the lateral pressure is identical during both sets of tests.

ICE STRENGTH OF VESSEL. The ability of a vessel’s hull structures and the elements of its running and steering gear that come into contact with ice to resist the loads caused by the ice without damage and residual structural deformation.

ICE STRUCTURE. The specific features of an ice mass influenced by the shape, dimensions, interlocation, and orientation of its crystals. The following are important elements in describing ice structure

crystal size - small-grained, medium-grained and large-grained;

grain size distribution - uniform-grained and non-uniform-grained;

crystal shape - allotriomorphic (irregular shape), parallel-fibrous, prismatic, lamellar;

C-axis positions relative to a freezing surface. The following orientations are common:

polar (C-axes of crystal are perpendicular to the freezing surface);

belt-like (C-axes are parallel to the freezing surface; i.e., random in the horizontal plane);

chaotic (position of C-axes at random angles to the freezing surface) and

spatially-ordered (in the horizontal plane but with a strong preferred direction).

composition-–fresh ice, brackish ice and sea ice;

A knowledge of ice structure allows one to examine the possibility of anisotropy in the various properties of ice.

ICE SURVEY DATA. The values of physical parameters which characterize the state of an ice sheet. Information on the state of various ice-related objects presented in a format designed for further processing.

ICE TEXTURE. An aspect of ice structure controlled by the spatial and size distributions of air, mineral, and organic inclusions in the ice. When considering air inclusions, ice is subdivided into monolithic (free of visible inclusions) and porous (containing inclusions that may have uniform, stratified, and vertical-fibrous distributions). Their sizes may be described as small-bubbled (inclusions smaller than 0.2 mm), medium-bubbled (inclusions of 0.2 to 0.5 mm in size), big-bubbled (inclusions of 0.5 to 1.0 mm in size), and big-cavity ice (inclusions that exceed 1.0 mm in size). The shape of inclusions may be oval, pipe-shaped, branched, and transformed.

As regard to origin, inclusions are subdivided into primary (autogenic), secondary (xenogenic) and texture-disturbed (cataclastic). In the picture you can see the transformation under the influence of radiative heating in the spring of primary cylindrical and branch-type air inclusions.

ICE TONGUE. A floating part of a glacier which projects out into the sea.

ICE TRANSPARENCY. An ice property that is defined by the ratio of the radiative flux that has passed through the ice with no change of spreading direction and the radiative flux entering the ice as a parallel beam.

ICE TRANSFER BY CURRENTS. Ice drift caused by the effects of either permanent or transient ocean currents.

ICE UNIFICATION. A decrease in the distances between ice-floes resulting in an increase in the ice compactness up to a value of 10 points.

ICE VISCOSITY. A property of ice that characterizes its resistance to the development of residual deformation when subjected to external forces. Viscous ice flow is observed at stresses lower than the yield limit and is characterized by the fact that with time deformation speed decreases due to the stress decrease and ultimately becomes zero. In the established process of shear strain formation, this quasiviscous (as with fluids) process is characterized by an effective viscosity or plastic viscosity where ts is the effective shear stress, tE is the elastic limit, and is the relative shear deformation rate.

ICE VISCOSITY INDEX (INTERNAL FRICTION COEFFICIENT). The coefficient of ice viscosity is defined by the tangential force F which has to be applied to a unit area S of a sheared layer of ice in order to maintain its laminar flow at a constant strain rate .

where is the shear stress.

Viscosity coefficients determined by static methods, e.g., by applying torsion, flexural, shear and tensile deformations are called static viscosity coefficients. Values of determined by static methods vary over a very broad range (from 109 to 1015 Pa·s) and it has been difficult to perceive any regularity in this variation. Therefore, can be considered to be a conditional parameter which characterizes the ratio of the stress to the creep rate under a given deformation speed, and at a given moment of time.

According to the results obtained by a number of authors ice viscosity does not satisfy Newton’s law due to the lack of linear dependency between the stress and deformation rate.

ICE WINDOW. An area of thin ice surrounded by thicker, and therefore, darker ice (as seen from below). These features have also been referred to as skylights in English.

ICE YEARBOOK. An annually published collection of ice observations obtained from various observation platforms (shore, island, aircraft, ships, satellites, etc.)

ICING. Icing is the process of ice growth on the surface of the above-water parts of vessels ( Photograph 44), hydrotechnical constructions, information buoys, etc.

ICING PARAMETERS. The values that define the time and the intensity as well as the start and the end of the icing process.

> > Start (end) of Icing. The time when the ice initially forms (or disappears) on the surface of an above-water project or its components.

> > Linear Speed of Ice Growth. The ice thickness increase per unit time. It is measured in m/s.

Volume (Mass) Speed of Ice Growth. The volume (mass) of ice accumulated on a project during a fixed time interval during an icing event. It is measured in m3/s.

IMPACT VISCOSITY (SPECIFIC ENERGY OF ICE DESTRUCTION). A parameter characterizing the ice resistance to impact loading that, if the collision energy is sufficiently high, results in localized deformation and the fracturing of a certain ice volume close to the contact zone. The impact viscosity may be estimated with the help of the energy of bending destruction of a notched sample on a pendulum impact testing machine (Charpy pendulm). It is expressed in J/m2 and is defined as the ratio of the energy to the cross sectional area of the cut. The specific energy of destruction is evaluated as an impact energy attributed to the volume of fractured ice (J/m3) or to the mass of crushed ice (J/kg).

INDEX OF LIGHT ATTENUATION BY ICE. The reciprocal of the distance at which a narrow parallel beam of light propagating in homogeneous ice is attenuated to 1/2.73 (i.e., 1/e) times its original value as the result of absorption and scattering.

,

In the above relation is the radiation flux absorbed and scattered in an elementary layer .

INDEX OF LIGHT REFRACTION BY ICE. The index that characterizes the decrease in the intensity of a light wave as it travels through ice as compared with through a vacuum (an absolute index of radiation absorption by the ice) or with another substance (a relative index of radiation absorption by the ice).

An ice crystal is uniaxial, optically positive, and has a property of double beam refraction.

For the ordinary beam, the index of ice absorption at -3°C changes from 1.306 to 1.318 as a function of the wavelength. For an extraordinary beam under the same conditions, the index of ice absorption changes from 1.307 to 1.326.

INDEX OF LIGHT SCATTERING BY ICE. An index of the attenuation of a beam of light passing through ice as the result of scattering on heterogeneities within the ice. The index is the reciprocal of the distance at which a monochromatic radiation flux propagating in homogeneous ice in the form of a parallel beam is attenuated to 1/2.73 (i.e., 1/e) times its original value:

,

where is the flux scattered in an elementary layer .

INDEX OF RADIATION ABSORPTION BY ICE. The reciprocal value of the distance at which a monochromatic radiative flux propagating in homogeneous ice as a parallel beam is attenuated by absorption to 1/e (i.e. 1/2.73) of its original value.

The intensity of a light wave after passing through the ice layer with thickness l is connected to the intensity of the wave at the layer entrance by the following correlation:

,

where is the index of radiation absorption by the ice which depends on the frequency of the light and on the peculiarities of the structure of the ice.

,

Here is the radiation flux absorbed in elementary layer .

INDICATRIX OF LIGHT SCATTERING BY ICE. A measure of the angular distribution of light scattering in a given direction with the total scattering coefficient normalized to unity

where g is the angle of incidence of the light on the ice volume and s is the scattering coefficient.

INERTIAL MOTION OF ICE. A periodic change in the velocity of ice drift with the period approximately equal to where

and is the angular velocity of the Earth’s rotation, and is the latitude of the ice.

The inertial motion of ice occurs as a result of changes in the frictional stress of the wind at the air-ice interface. In the Arctic basin, the period of inertial changes in the ice motion is approximately 12 hours.

INFRARED RADIATION OF THE ICE (SNOW) SHEET. Electromagnetic radiation in the infrared portion of the electromagnetic spectrum originates from a thin surface layer (3 to 184 microns thick) of ice (snow). Such infrared radiation is also called the self-radiation of an ice (snow) sheet.

INTERACTION BETWEEN ICE FLOES. The mechanical interaction between ice floes may result in changes in the both velocity of the floes as well as in their geometry through hummocking.

INTERNAL FRICTION OF ICE. This ice property measures the irreversible transformation into heat of mechanical energy accumulated in the ice as the result of deformation. Note that ice deformation upsets thermodynamic equilibrium. Two groups of phenomena are distinguished: anelastic (ice behaviour when only small deviations from Hooke’s Law occur) and viscous.

ISOBARIC ICE DRIFT. Ice drift parallel to the contours (isobars) of the pressure field of the atmosphere at a speed proportional to the pressure gradient.. Here it is assumed that the direction of isobars coincides with the direction of geostrophic wind.

DEVIATION ANGLE OF ICE DRIFT TO THE WIND. This parameter describes the angle between the direction of ice drift and the isobars, where the latter is assumed to be equal to the direction of the geostrophic wind.

ISOBARIC COEFFICIENT. The proportionality coefficient k between the horizontal pressure gradient and the drift speed. An isobaric coefficient enables one to calculate the ice drift rate W from the pressure gradient :

Isobaric coefficients and deviation angles vary greatly in time and space because of the complicated structure of drift fields and changes in wind currents.

J

JUSTIFIABILITY OF ICE FORECASTS. An average statistical value of the justifiability considering all ice forecasts of a given timeliness for a specific time period.

K

L

LABORATORY ICE. See modeled ice

LARGE-SCALE ICE DRIFT. The motion of ice as characterized on a spatial scale of hundreds to thousands of kilometers.

LEAD. Any fracture or passageway of considerable lateral extent through sea ice that is wider than 1 m (Photographs 29, 45). Leads are formed by the widening of cracks ( Photograph 25) as the result of stresses within the ice. [In the literature the distinction between a crack and a lead is rather vague. The WMO Nomenclature suggests that the distinction should be based on whether or not the feature is navigatable by a surface vessel. We suggest that the criteria of non-jumpable is more useful particularly for individuals operating on the ice surface.] Leads can be subdivided similarly to cracks in accordance with their genetic and morphologic features:

The age - fresh (cracks containing either clear water or primary ice types), young (cracks covered with young ice), old (cracks covered with winter ice).

The length - intrablock (up to 5 km long), interblock (up to 100 km long), main (some hundreds of kilometers long).

The penetration depth - gaping, unopened.

The shape of crack edge - smooth, uneven, notched.

The shape along their lateral extent - straight (linear, wedge, slot-type), bent (arc, link, round-type), fractured (zigzag, sinusoidal, cycloid-type).

LIFE DURATION OF ICEBERG. The time period from iceberg formation until its complete destruction. For example, the average life of a Greenland iceberg is 3 years, and in the Antarctic - 2 years. The longest lifetimes are experienced by icebergs that have either shoaled or have drifted into regions where the current patterns are closed.

LIFETIME OF AN ICE FLOE. The length of time between the formation of a particular floe and its destruction either by completely melting or by it being split by a lead.

LIMIT OF THE MECHANICAL ENDURANCE OF ICE. A strength characteristic of ice that can be defined from the results of experiments in which samples are tested using cyclic, and more often, dynamic loading. Here, the load is called dynamic when significant particle accelerations are observed in the deformed body . For example, they occur as a result of impacts and also as free or forced oscillations. With time these regular, repetitive sign variable stresses result in the formation of tiny cracks in the ice that then gradually increase in size and lead to the destruction of the sample. As the number of stress change cycles increases, the strength limit (i.e., limit of the mechanical endurance of the ice) decreases. Thus, under the effect of a dynamic sign-variable load, the strength of ice, as well as of other solids, may be characterized by their endurance limit sr ( i.e. the highest stress that the ice may repeatedly endure for some specified number of times (e.g. 106) without failure. There is very little published data relating the results of large amplitude cyclic loading of ice to its fatigue failure.

LIMIT OF LONG-TERM ICE CREEP. The stress (see Figure 7) at which the deformation does not change (). At stress amounts of , the ice does not fail. At the yield "platform" (the portion of the curve at a level of 0.7, ( Figure 12) does not have time to form; there is no shear deformation corresponding to the established creep and progressive creep occurs rapidly as an avalanche, this is the reason for brittle ice failure. In this case, the term "ultimate strength" sbrmay be applied, which is sometimes called the brittle strength of ice.

LIMIT OF LONG-TERM ICE STRENGTH OR CREEP LIMIT. The conditional stress ss, that after a period of time ts (referred to as the time to failure) brings the deformed ice to the final stage of tertiary creep when its deformation rate (and, correspondingly the deformation) goes to infinity ( and , see Figure 7).

LOCAL NONUNIFORMITY OF ICE SHEET. The spatial nonuniformity of an ice sheet within the boundaries of an ice formation (ice field, ice floe, conglomerated ice). The spatial scale of non-uniformity has a random character and is determined by the continuous deformation of the ice sheet.

LOGARITHMIC DAMPING FACTOR (logarithmic decrement). A quantitative characteristic of the rate of decay of free oscillations in ice samples which usually are induced with the sample fixed at one or two points). The logarithmic decrement is defined as the logarithm of the ratio of the amplitudes during two subsequent oscillations.

M

MAPPING OF ICE CONDITIONS. The mapping of observational results (visual, photographic, or with the help of radar or satellite systems) onto an blank map. Mapping is typically carried out by using a set of conventional symbols. Boundaries of areas having uniform ice characteristics are commonly plotted.

MATHEMATICAL MODELING OF THE ICE COVER. A description of the current state as well as anticipated changes in the condition of an ice cover with the help of mathematical dependencies that take into account the phenomena of primary importance for a given task as well as their interrelations.

Depending on the type of mathematical description of the object under investigation and the methods used in determining unknown parameters, mathematical models of an ice cover can be divided into four categories: statistical, hydrodynamic, thermodynamic and mixed.

STATISTICAL MODELS. Models which describe processes with unknown causal relationships via the use of random processes.

Depending on the type of functions used to describe processes, statistical models can be further subdivided into empirical-statistical and physico-statistical.

Empirical-statistical models. Models based on an approximation of the determined components of a random processes set with the help of polynomial, trigonometric or exponential functions.

Physical-statistical models. Models in which the description of multifactor random processes is made in terms of random functions (spectral, regression, etc.).

HYDRO-THERMODYNAMICAL MODELS OR MIXED MODELS. Models describing multi-parameter deterministic processes occurring in an ice sheet. Model descriptions are usually made in terms of sets of hydrodynamic and/or thermodynamic equations.

HYDRODYNAMICAL MODELS. Models describing the dynamics of an ice sheet in terms of a set of differential equations derived from continuous media equations.

MECHANICAL PROPERTIES OF ICE. The ability of ice to resist deformation and failure in combination with its ability to undergo elastic and plastic deformation under the impact of internal and external forces.

The mechanical properties of ice are described in terms of its elastic, plastic and strength characteristics, which are not material constants because they largely depend on the structural peculiarities of the ice, on its composition, on the form and the size of the stressed body, on the loading rate, and the surface conditions of the sample, etc.

MECHANICAL STRESSES IN ICE. A measure of the internal forces acting per unit area of a cross-section of ice under the impact of an applied external force.

In order to analyze the mechanical stresses at a point M in a body, one must construct a section (plane) passing through this point. The interaction between body parts separated by the section is measured in terms of forces. Assuming that area element dS including the point M experiences the force dF, one can calculate the vector of the mechanical stress acting on the area element located at point M:

P = (dF)/(dS)

The components of this vector are as follows: the projection on the direction perpendicular to the section is called the normal stress and designated s, the projection on the direction tangential to the section is called tangential stress and designated t. The above parameters are related as follows

.

The set of all possible stress vectors connected with point M characterizes the stressed state at this point. This state is fully described by the symmetric stress tensor

where the components of stress tensor are expressed in the coordinate frame x, y, z ( Figure 13).

Components of stress tensor characterize mechanical stresses on the faces of an infinitely small parallelepiped which includes point M. In the equations above, we use a system of notations which one usually finds in technical literature. In some cases, one may find it more convenient to use tensor notation in which the components of the stress tensor are expressed in the form , where i,j = 1, 2, 3.

MESOSCALE DRIFT OF ICE. The drift of ice considered at spatial scales ranging from several kilometers to dozens of kilometers and over time periods lasting from a few hours to several days.

METAMORPHISM OF ICE SHEETS. Changes in the ice structure as the result of the effect of its temperature (thermal metamorphism) or pressure (dynamic metamorphism). Metamorphic transformations usually take one of the following forms: recrystallization processes which occur in the solid state, regelation processes which involve melting and refreezing, and sublimation processes which involve solid-gas transitions. All of these transformations commonly include the surface migration of both substances and crystal boundaries.

MICRORELIEF OF SEA ICE. A variety of small-sized secondary irregularities that may occur on the surfaces of the major elements comprising the gross ice topography. The dimensions of microrelief elements range from several millimeters to dozens of centimeters.

ICE STALACTITES. Ice features that occur in the form of hollow, thin-walled tubes and that extend downward from the bottom of sea ice sheets (Photographs 46a and 46b). These features only form in the winter when the ice is actively growing. Ice stalactites are located at the bottoms of the brine drainage tubes which localize the concentrated streams of cold brine that drain from the ice into the sea. As the temperature of this brine is below the freezing point of seawater, an ice stalactite gradually develops. In young ice, 3 - 4 ice tubes per square meter of ice surface may form. In the vicinity of fresh cracks, young stalactites are located at distances of 8 - 10 meters from the edge of the crack. When the current in the layer close to the ice exceeds 4 - 5 m/s, the streams of brine leaving the ice are immediately well mixed into the underlying water column and stalactites are not formed.

ICE WAVES. A microrelief form that develops as the result of ablation on the under-water surface of sea ice. Wave-like features develop in the ice as the result of thermal erosion of the ice by the turbulent current at the ice-water interface. This type of microrelief can be observed on the streamlined lower parts of hummocks and on the sides and lower surfaces of thick ice. The amplitudes of ice waves may be 5 to 10 centimeters and their lengths may reach several tens of centimeters. These features also commonly occur on the underside of river ice during the spring melt period.

INITIAL ABLATION MICRORELIEF. Small, oval cavities formed on the lower surface of sea ice because of faster melting in the vicinity of structural and textural irregularities. Clusters of phytoplankton developed during the summer season fill up the initial ablation holes, and as they adsorb sun light, help to further such nonuniform melting of the lower ice surface. By the end of the melt period, these cavities may have diameters of several dozen centimeters and depths of 15 to 20 centimeters.

OPEN BRINE DRAINAGE CHANNELS. At the end of the melt period, the brine drainage channels within the sea ice become quite enlarged assuming a cone-like shape in which the broad lower portion of the cone can have diameters of 15 - 20 cm while the narrow upper portion is only a few centimeters wide. These microrelief elements are characteristically found in first- year ice.

SERRATE ICE. Groups of closely spaced conical cavities and projections which form on the bottom surfaces of pools in multiyear ice. The fact that phytoplankton growth is favored by the better illumination in this part of the lower ice surface and consequently fills these holes while, at the same time absorbing the incoming radiation, helps in the formation of this type of microrelief.

SKELETON LAYER. A microscopically rough layer located at the lower surface of growing sea ice formed by the end of the ice crystals directed perpendicular to the surface of ice. Skeleton layer thicknesses are believed to depend on the rate and conditions of ice growth. Its thickness varies from fractions of a millimeter to several centimeters.

This type of under-water ice surface microrelief is observed during the winter season at depths not exceeding 8 - 10 meters.

SMOOTH ICE. A qualitative term describing the state of an ice surface following the complete disappearance of the skeleton layer. This condition is a clear sign that melting is occurring at the sea ice / seawater interface.

MODELED (LABORATORY) ICE. Ice grown under laboratory conditions typically for the purpose of obtaining a test material with specific structural and physical-mechanical properties.

Current methods of ice preparation enable one to reliably reproduce ice with a uniform structure. Modeled ice typically corresponds to natural ice of A2 and B4 categories according to N. V. Cherepanov’s classification ( Figure 3). The term "modeled" ice was introduced by V.V. Lavrov.

MIXED ICE. Ice formed on a surface of an object from both atmospheric and hydrospheric water.

MODULUS OF DILATATION. A modulus obtained under conditions of (bulk) compression by normal stresses, i.e., hydrostatic compression. The modulus of dilatation K is determined as the ratio of the normal stress s to the relative bulk compression which is given by .

The modulus K characterizes the ability of ice to resist changes in its volume while maintaining a constant shape. Normally, the values of K exceed those of Young’s modulus by several percent. However, for some types of highly porous multiyear ice, K may be smaller than E.

MODULUS OF ELASTICITY OF ICE (YOUNG’S MODULUS), E. The parameter E is determined as the ratio of the normal stress s to the relative elongation e caused by the stress in the direction of stress.

The modulus of elasticity characterizes the ability of ice to resist tension.

ACOUSTIC (ULTRASONIC, SEISMOACOUSTIC) MODULUS. A dynamic Young’s modulus determined by measuring the density of the sample and the velocities of the longitudinal and transverse waves over small distances (tens of centimeters in the case of the pulsed ultrasonic method) and over larger distances (tens to hundreds of meters in the case of the seismoacoustic method).

AVERAGE INTEGRAL (EFFECTIVE) YOUNG MODULUS. Young’s modulus as determined in experiments performed on large samples (i.e., samples with horizontal dimensions larger than the thickness of ice sheet under study).

COMPLEX ELASTICITY MODULUS. The modulus of elasticity as determined from the relation between the amplitude of a periodic stress oscillating at frequency and its strain component

The tangent of the angle gives the lag in the strain behind the stress and provides a measure of the internal friction. Its value is equal to the ratio of the imaginary part E2(w) to the real part E1(w)

If we denote and we get

where the difference

characterizes the rate of relaxation and is called the defect in Young’s modulus.

DYNAMIC MODULUS OF ELASTICITY . The modulus of elasticity as determined from the ratio of the stress to the deformation component in phase with the stress. Its value is determined from the expression

where

and

NONRELAXING MODULUS OF ELASTICITY. The dynamic modulus of elasticity which gives the relation between the final changes in s and e when these changes occur sufficiently rapidly so that no relaxation takes place

RELAXED MODULUS OF ELASTICITY. The modulus of elasticity determined in situations when the relaxation process has ceased. In this case, the following relation holds:

En = ER2 ´ (ts /te)

where is time of stress relaxation at constant strain and is the time of retardation, i.e., a parameter which characterizes the rate of strain increase under constant stress.

SECANT MODULUS. The average value of the derivative of the s versus e curve ( Figure 14). In cases of rapid deformation or at low temperatures the secant modulus is large. In contrast, at slow deformation or at high temperatures, the curvature of the function becomes considerable and the secant modulus becomes smaller than the true or instantaneous modulus:

TRUE OR INSTANTANEOUS YOUNG’S MODULUS. A parameter describing instantaneous elastic deformation, e.g., in an idealized experiment on uniaxial compression when sudden stress causes an infinite rate of stress change and an infinite deformation rate.

True Young’s modulus can be defined as the slope of the tangent to the curve (see the diagram in Figure 14) at the origin of the coordinate frame . True Young’s modulus is also sometimes called the initial tangent modulus.

MONOCRYSTALLINE ICE. When applied in a strict sense, the term monocrystal refers to a separate single crystal of ice. In this sense, the expression is commonly used to describe fairly large-sized crystals of ice with lateral dimensions in the range of 10 to 100 cm or more. However, the term is occasionally also used more loosely to refer to ice areas where all the crystals have their C-axes pointing in essentially the same direction.

MORENITSA (Russ.). Sea water which occurs on the surface of sea ice as the result of the depression of the upper ice surface below sea level. Such depressed surfaces are frequently caused by the weight of a thick accumulation of snow. [There is no equivalent expression in English.]

MORPHOMETRIC CHARACTERISTICS OF ICE SHEET RELIEF. Quantitative measures of the different aspects of sea ice relief features obtained by means of visual or instrumental monitoring ( Figure 15).

DEPTH OF A SURFACE POND Hw = hw – hi. The thickness of a water layer in a pond on the surface of a floe.

DIMENSIONS OF ICE FRAGMENTS IN HUMMOCKS Lfr. The average lengths of hummocky ice blocks as measured in the planes oriented perpendicular to the thickness of the block.

HUMMOCK DRAFT (HUMMOCK RIDGE DRAFT) zt. The vertical distance between a point on the bottom of a hummock and sea level.

HUMMOCK (HUMMOCK RIDGE) HEIGHT hhum. The vertical distance between a point on the top of a hummock or from any point on a hummock’s ridge and sea level.

ICE DRAFT zi. The vertical distance between a point at the base of the ice sheet and sea level. This measurement may be made by a variety of techniques. These include measurements using bore-holes, observations by a diver using hydrostatic leveling techniques, and hydroacoustic sounding of the lower surface from submarines or other automated underwater vehicles.

Ice height hi. The vertical distance between a point on the upper surface of an ice sheet and sea level; the freeboard of the ice surface. This elevation difference may be measured by a variety of techniques. Most direct observations use a bore hole through the ice or measurements made on the edge of the floe. Other possibilities include optical leveling and laser profiling.

ICE THICKNESS. Hi = hi + zi. The total ice thickness which equals the sum of the ice height and the ice draft at any given point.

SNOW SURFACE HEIGHT hsn. The vertical distance between the upper surface of the snow and sea level; the snow surface freeboard

THICKNESS OF ICE FRAGMENTS IN HUMMOCKS Hfr. The thickness of an ice block in a hummock. In cases where the hummock was formed by significant amounts of shearing, the thickness of the ice fragments decreases by .

THICKNESS OF THE SNOW SHEET. Hsn = hsn - hi. The thickness of the snow layer is the difference between the snow surface height at a given point and the ice height at the same point.

WATER HEIGHT OF A SURFACE POND hw. The vertical distance between the level of the water surface on a melt pond not connected with the sea and sea level.

N

NASLOOD (Russ.). Thin ice formed as a result of the freezing of melt water on the surface of gullies, thawed patches and in ponds on the ice (Photographs 8 and 56). The resulting ice frequently has very low salinities. [There is no equivalent expression in English.]

NATURAL HYDROLOGIC PERIOD. A period of time during which a large-scale atmospheric process develops over a frozen sea resulting in a specific circulation pattern of the water and ice.

NATURAL ICE. Ice that has formed as the result of naturally occurring processes. Natural ice can be subdivided into three classes based on the nature of these processes: congelation, sedimentary, and metamorphic. The ice in these three classes can also be subdivided on the basis of the formation location into atmospheric, terrestrial, floating, and subsurface ice and on the basis of age into seasonal and old. If the composition of the floating ice is considered, it can be further subdivided into sea ice, brackish ice, and fresh-water ice. Floating ice can be further subdivided into sea, lake, river ice, and icebergs.

AERATED ICE. Ice saturated with air bubbles. It is formed when water containing dissolved air freezes rapidly or when dry, finely-dispersed ice containing large amounts of air between the ice particles sinters together.

ANCHOR ICE. The formation of intrawater ice on stones, rocks, or separate metallic items located on the seafloor. Anchor ice typically forms on the bottom of offshore shoals during the late autumn.

ATMOSPHERIC ICE. The ice that forms in the air or on different surfaces from atmospheric water vapor. Included are ice particles suspended in the atmosphere and fallen on the surface, as well as ice crystals and solid deposits formed on objects.

BLACK ICE. Ice formed due to the freezing of fresh water pools containing only small quantities of scattering impurities. This ice has a dark, almost black color. It corresponds to the ice of A1, A2, A3 types. This term is also used in the foreign literature.

BRACKISH ICE. Ice formed from water that has salinities between 1 and 24.7‰. The resulting ice types have not been extensively studied.

CLEAR ICE. Ice that does not contain admixtures in the form of air bubbles, brine cells, particles of salts, soil, or other mineral or organic substances.

COATING ICE. Ice that forms on the surface of coastal rocks and stones as a result of wave activity. It is a product of the icing process development.

CONGELATION ICE. Strictly speaking, congelation ice is any ice that forms from the freezing of bulk fresh water or seawater. It is characterized by a variety of forms and is extremely wide spread.

However in practice, the expression congelation is commonly used to identify ice that formed via a classical Stefan 1-dimensional growth scenario where the heat liberated by the formation of the ice is conducted away upward through the overlying ice sheet.

CONGELATION-FRAZIL ICE (HYDROGENIC or WATER ICE). The ice that forms when intrawater frazil crystals freeze together as the result of congelation ice formation.

FRAZIL ICE (SHUGA). An accumulation of primary plate-like and acicular ice crystals that have formed within the water column as the result of supercooling. When the term shuga is used it implies that the frazil has formed into spongy white lumps.

FRESH ICE. Ice formed from water containing less than 1‰ of sea salts. It contains negligible amounts of included brine and solid salts.

FRESH-WATER ICE. Ice formed from fresh water in rivers, lakes, reservoirs, and on local near-shore areas of the sea.

ICE-MOUND ICE. A type of congelation ice which forms by the freezing of water layers located on the surface of ice sheets. It has a well-defined textural stratification parallel to the freezing surface. Its surface characteristically has a slight dome-like shape as the result of deformation caused by the increase in the pressure produced by the volume increase during freezing (the so-called frozen milk bottle effect) ( Photograph 56).

INJECTION-ICE-MOUND ICE. Congelation ice that results from the injection of water through intercrystalline spaces in the upper portion of an ice sheet. It has the same general structure as ice-mound ice. The primary difference between these two terms is that injection-ice-mound-ice forms as the result of the freezing of seawater as opposed to fresh water.

LAKE ICE. Ice that forms on lakes or reservoirs. Here the term "lake ice" refers any ice type forming on inland bodies of standing water. Although the vast majority of lake ice is "fresh", it is possible to have lake ice form on saline lakes and have salinities in excess of typical sea ice values.

REGELATION ICE. Ice formed due to the process of thermodynamic metamorphism as a result of the partial melting of ice crystals and the subsequent refreezing of the thawed water.

RIVER ICE. Ice formed on rivers due to the solidification of water mainly under the conditions of a current. River ice belongs to group A of the structural and genetic classification of natural ice (see Figure 3).

SALT-WATER ICE. Ice formed from water that has a salinity of over 24.7‰. The process of ice formation from salt-water differs appreciably from ice forming from brackish water which has a salinity < 24.7‰.

SEA ICE.

(1)The ice forms as the result of the freezing of sea water.

It should be noted that in literature, the expression "sea ice" is widely used not only to characterize the ice sheet as a natural object in a specific sea, but also ice as a physical body in relation to the entire sea area. This is incorrect, as long as varying hydrometeorological conditions cause varied ice types that sharply differ in their structure and physical properties to occur in the same sea.

(2)The ice or ice sheet that forms on or in the sea.

In this case, the name "sea ice" reflects the water body on which it has been formed, receiving a geographic orientation.

SNOW-WATER ICE (infiltration-congelation ice). Ice formed due to the freezing of water (thawed, rain, sea water) that has penetrated into the snow cover.

WATER-SNOW ICE. Ice that has formed by the freezing of slush on the upper surface of an ice sheet.

NICHE. See Iceberg, Wave-Cut Terrace.

NON-ELASTICITY OF ICE. There are a number of phenomenological theories generally describing the non-elastic or relaxation properties of solids. As applied to the ice, the most frequently used is the method of rheological models in which its behavior is described by state equations through the use of stresses and deformations and their time derivatives.

NUMBER OF ICEBERGS. The total number of icebergs in a given sea or ocean area as of the time of observation.

NUMERICAL ICE FORECASTS OF LOW TIMELINESS. Short term ice forecasts typically prepared from 4 to 8 days in advance of use. These forecasts are drawn up for all arctic seas from June through September and are sent weekly to customers by phototelegraph.

The spatial resolution of numerical ice forecasts of low timeliness is typically 50-70 km. For separate water areas of the arctic seas, detailed forecasts with spatial resolutions of 20-25 km are also currently provided.

Numerical ice forecasts of low timeliness are charts showing the expected distribution of ice thicknesses and the total ice compactness. The direction and speed of prevailing ice drifts and regions of compression are also identified.

NUMERICAL LONG-TERM ICE FORECASTS. Ice forecasts of which the shortest term is from 1 to 4 months. The spatial resolution of long-term numerical ice forecasts is typically 70-75 km.

Long-term numerical ice forecasts are developed separately for the winter and the summer periods. For the winter period, these forecasts are provided in the form of charts giving the expected distribution of ice thicknesses, the isochrones of stable ice formation, and the geographic positions of old ice borders or of the edge of the ice. For the summer period, they are provided in the form of charts of the expected distribution of ice thickness and compactness. Tables of the expected average decadal values of ice formation and the expected boundaries of ice massifs are also issued.

O

OPEN ICE EDGE. A transition zone comprised of open or very open (low compactness) ice located between an area of pack ice and open water ( Photograph 38).

OLD SNOWSHEET. Fine to medium grained snow that is evenly distributed on the surface of an ice sheet. The presence of complex bedding patterns in the snow indicate that deposition has occurred during several different storms.

OPTICAL PROPERTIES OF ICE. Ice properties that describe its interaction with electromagnetic waves occurring at optical frequencies. Included are the wide spectrum region adjacent to the visible frequencies, an ultraviolet region including X-rays, and an infrared region extending up to radio waves in the millimeter band.

ORTHOTROPIC CRYSTALLIZATION. An expression describing the type of crystal growth commonly occurring in undeformed sea and lake ice sheets where the developing ice crystals are mutually constrained as they advance in the direction of the heat flow.

OUTLET GLACIER. A glacier through which the ice which has developed in a commonly large accumulation region is carried out of that region. Outlet glaciers frequently transverse mountain barriers that serve to define the accumulation region. In the northern hemisphere, in regions such as Greenland, most outlet glaciers end in the sea where they produce icebergs that have a large variety of different shapes and sizes. In the Antarctic, outlet glaciers commonly flow into ice shelves which then ultimately calve into the sea producing tabular icebergs

P

PERENNIAL ICE. See multi-year ice.

PERMISSIBLE ERROR OF ICE FORECASTS. An error value conditionally defined on the basis of their timeliness.

PERMISSIBLE SPEED OF VESSEL NAVIGATION IN ICE. The maximum speed at which a vessel can safely transit a given area of sea ice without sustaining structural damage to the hull or propulsion system.

PHASE OF ICE SHEET DEVELOPMENT. One of the qualitatively different states of ice sheet development as characterized by its physical properties and behavior. For example: the phase of fast ice formation, etc.

phase VELOCITY of elastic oscillations in ice.(see also Sound Velocity in Ice). The velocity with which the phase of monochromatic sinusoidal waves moves in ice:

,

where T is the period, l is the wavelength, and is the wave phase.

Constant phase moves at the velocity C = dx/dt = l /T. This is the phase velocity.

PODSOV ( Russ). Pieces and plates of ice pushed under an ice sheet as a result of rafting and hummocking (Photographs 47 and 50). [There is no equivalent English term.]

POINT. A conventional unit for quantitative and qualitative evaluation of ice phenomenon or characteristics (e.g., ice cohesion, hummocking, etc.). In practice, 3-, 5-, and 10-point scales are normally used.

POISSON’S RATIO OF ICE. A parameter characterizing the elastic properties of ice and defined by the ratio of the absolute value of the relative transverse deformation to the relative longitudinal deformation:

where are deformations along the corresponding axes.

For isotropic ice . For an ice monocrystal the properties are anisotropic and . In this case, Poisson’s ratio is usually assumed to be equal to 0.33.

POLLUTANTS. Naturally occurring or artificially produced materials that are deemed to be undesirable and that do not typically occur in the setting or in the material under study. In the case of ice, the polluting material may either penetrate into the ice or be concentrated and transported on its upper surface of the ice. Pollution levels that exceed maximum permissible safe concentrations may result.

ANTROPOGENIC POLLUTANTS. Small fractions of air sprayed fertilizers, insecticides, and defoliants, oil spills, and other industrial wastes deposited on or in the ice.

TERRIGENOUS POLLUTANTS. Wind-borne pollutants that are transferred onto the ice ( Photograph 37).

THALASSOGENIC POLLUTANTS. Pollutants contained in wind-generated sea water sprays that are transferred to the ice surface ( Photograph 42).

VOLCANIC POLLUTANTS. Substances normally existing within the interior of the earth and transferred onto the ice surface as the result of volcanic eruptions.

POLYNYA. (Russ.). A stable area of > 5 x 5 km in size composed of open water, different primary ice types, glass ice (nilas, Russ.) of any compactness, or a zone of rarified ice or of any other age gradation occurring within a sea ice area having a compactness of over 3 points or between such an ice area and the coast.

EPISODIC (UNSTABLE) POLYNYA. A polynya whose probability of existence within a certain time period is less than 0.50.

OFF-ESTUARY POLYNYA. A polynya formed in the spring between the river’s mouth or delta and the fast ice.

OCEAN OR OPEN SEA POLYNYA. A polynya located offshore among pack ice (e.g. the Weddell Sea polynya).

OFF-FAST-ICE POLYNYA. A polynya formed between the fast ice and the pack ice ( Photograph 11).

OFF-SHORE POLYNYA. A polynya formed between the shore or ice barrier and the pack ice. In the second case, the term "off-ice polynya" would be correct.

STABLE POLYNYA. A polynya whose probability of existence within a certain time period is from 0.50 to 0.75.

STATIONARY POLYNYA. A polynya whose probability of existence within a certain time period is more than 0.75.

PORT ICE-BREAKER. An ice-breaker that operates near ports, terminals, and crossings, as well as in their approach zones.

PRESSING WIND. The wind that imparts a shore-directed component to the wind-driven drift of pack ice.

PRESSING-OFF ICE DRIFT. Ice drift when its normal component is directed offshore.

PRESSING-ON ICE DRIFT. Ice drift when its normal component is directed toward the shore.

PRINCIPAL CRYSTALLOGRAPHIC AXIS (C-AXIS). See Optical axis of crystal. The direction in hexagonal crystals such as ice along which no double refraction occurs (see Figure 1).

PROBABILITY OF FINDING ICE. A quantitative parameter characterizing the probability of finding ice in the sea. Here the notion of probability implies that one could, in theory, obtain an arbitrarily large number of observations of the ice conditions occurring under the same sequence of environmental conditions.

The numerical value of probability must, by definition, lie between 0 to 1. With an increase in the number of observations, the probability approaches the frequency of events.

PROTOCRYSTALLIZATION. The initial stage in the formation of free-growing crystals before they come into contact with one another and form aggregates.

PROVISION OF THE ICE FORECAST METHOD (P). The ratio of the justified forecasts (mj) and the total number of forecasts issued (nt). It is expressed in per cent

.

PUDDLE (Snezhnitza, Russ). An accumulation (pond) of water formed either from the melting of the snow cover resting on the upper surface of the ice or by the melting of the upper part of the ice sheet. In their initial stages puddles are simply localized patches of snow that has been saturated with water.

Q

QUIET ICE CONDITIONS. From the viewpoint of hydroacoustics this expression refers to the state of a local area of an ice covered sea that is characterized by a low mean statistical level of ambient underwater noise owing to the absence of nearby high level sound sources such as thermal cracking, hummocking, etc.

R

RAFTING. A type of deformation in which one sheet of ice slides over another ( Photograph 48). Although rafting can occur in ice of almost any thickness, it is most common in thin ice.

RASVODIJE (Russ.) (FRACTURE) A localized area of open water within consolidated ice with a rhombohedral, cresentic or lenticular shape formed during a period of slight shear pressure as the result of ice fields shifting along the line of a former main crack or lead ( Photograph 49). When refrozen during the autumn-winter period, the ice in a rasvodije grows very rapidly and frequently may be used as a runway.

RECOMMENDED STANDARD (TRADITIONAL) NAVIGATION IN THE ICE. A navigational route across the frozen seas of the world as specified in official documents regulating ice navigation.

REGELATION RECRYSTALLIZATION. The recrystallization of ice involving a transition through the liquid phase.

REINFORCED ICE. Ice with increased mechanical strength resulting from artificially introduced inclusions. It is typically produced by adding various solid materials (wood is frequently used) to freezing water or by freezing water over metallic grid-like frameworks (similar to the introduction of metal rods in reinforced concrete).

RELAXATION RELATED ICE OSCILLATIONS. Periodic ice deformation that occurs when ice is subjected to a constant horizontal compressive force. It occurs as the result of stress increases at a point where the ice sheet most directly contacts either an adjoining ice sheet or a ship or offshore structure. After the stresses have built up to certain critical values, either relaxation or ice failure occurs. In both cases there is a brief relaxation of stresses before the process repeats itself. This results in a number of relaxation oscillations which are accompanied by ice sheet pulsations and associated buckling with a periodicity of 10 sec and more.

RELAXATION TIME (FAST ICE PROCESSES). The relaxation time strongly depends on the microscopic characteristics of ice and, in particular, on mean parameters that characterize interactions between particles: the time and the distance l of the free path length of the particles.

The relaxation time of fast processes is described by the formula in which . Fast processes include dielectric relaxation, elastic and spin-lattice relaxation.

RELAXATION TIME (SLOW PROCESSES ). The relaxation time of slow processes is proportional to the dimensions of the system L and is large as compared with the mean free path time tc:

For instance, slow relaxation processes even out differences in temperature, pressure, mean deformation velocity and other characteristics of ice as a system. Such relaxation processes include viscous flow, diffusion, heat conductance, and electric conductance, etc.

In accordance with a Maxwell’s model of a solid body, the relaxation time of stresses in ice is a function of viscosity and shear modulus G:

Experiments show that the time of stress relaxation in ice varies from fractions of a second to several hours.

RELIABILITY OF ICE FORECASTS. The probability of a forecast ice event not exceeding an admissible error limit.

RELIEF FORMATION PROCESSES. The aggregate of dynamic, thermo-physical, and other processes resulting in the formation and further modification of macro and microrelief on ice sheets.

ICE CORRUGATING. A process of durable plastic deformation during bending which can occur without fracturing during the deformation of black and young ice. The result is a series of small, undulating two-dimensional corrugations that retain their corrugated shape indefinitely ( Photograph 15). Corrugations are usually observed on young ice occurring in recently refrozen former open water areas or channels located among thicker pack ice.

ICE HUMMOCKING. The process of breaking and local compression of ice at the points of contact between two drifting ice-floes or at the points of contact between an ice-floe and fast ice, land or fixed offshore structures. The compressive forces driving this process invariably result in large accumulations of ice fragments being heaped on the surfaces of ice sheets, shoals, etc., in the form of different hummocky formations. Such formations are the primary sources of macrorelief on the upper and low surfaces of ice sheets (Photographs 9, 13, 33, 34, 51).

ICE RAFTING. A process due to compressive forces where the edge of one floe overlaps the edge of an adjoining floe resulting in a region of two layered stratified ice (Photographs 3, 5, 48). This process may be repeated several times forming multilayered ice several meters thick.

ICE SHEET ISOSTASY. The term isostacy refers to the state of being in hydrostatic equilibrium. Although free-floating ice sheets are obviously in overall isostatic equilibrium, there are a number of processes that occur in natural ice sheets that produce locally non-isostatically balanced areas on ice floes. Examples are the formation of statically unbalanced hummocks, the non-uniform distribution of snow on the ice surface and particularly the formation of deep drifts in the lee of larger hummocks, and non-uniform ice ablation on some areas of the upper and low surfaces of an ice sheet.

ICE SWELLING. The formation of a rolling ice surface resulting from the freezing of ponds that have developed on the upper surfaces of ice sheets during melt periods (snezhnitza, Russ.) ( Photograph 56).

SMOOTHING OF ICE SHEET SURFACE. The process of gradual smoothing of large surface irregularities as the result of melting and weathering.

RELIEF OF ICE SHEET SURFACES. The characteristic relief of the upper and lower surfaces of ice sheets as reflected in the aggregates of micro and macro unevenness of different shapes, dimensions, and origin.

EVEN ICE. An ice sheet with flat upper and lower surfaces. Such ice sheets typically form under quiet, calm conditions in protected locations.

LAYERED ICE. Stratified ice formed as a result of rafting of the edge of one floe over another. In some cases that rafting patterns are complex achieving a gear-keyed or square wave shape referred to in English as finger rafting. Such rafting is typical of black and young ice. Multi-layered floes reaching thicknesses of 3 or more meters have been reported.

HUMMOCKY ICE. Piles of deformed ice resulting from local crushing and breaking of ice along the points or lines of contact between two adjacent ice floes, ice fields, or on the border between fast ice and pack ice (Photographs 9, 13, 33, 34, 50) .

HILLY ICE. A type of deformed ice resulting from multi-year metamorphic processes occurring in hummocky formations as the result of multiple melting and weathering events ( Photograph 13). Typical of old ice.

REMOTE SENSING METHODS OF SEA ICE STUDY (FúHJRJCVQXTCRBT). A combined method of remote analysis of ice sheet properties and their changes with the help of helicopters, aircraft, manned space stations, orbital satellites, and specially designed spacecraft equipped with a variety of remote sensing devices.

The use of remote sensing methods in the investigation of sea ice enables one to obtain a large body of information on this natural material on a regular basis. These methods provide powerful tools for monitoring changes in the sea ice cover that occur under the influence of both natural and anthropogenic factors. [Note that the phrase aerocosmic which is the direct translation of FúHJRJCVQXTCRBT occurs in many Russian translations instead of the more correct term remote sensing.]

INFRARED (IR) SURVEYS OF SNOW AND ICE SURFACES. The remote detection (normally made from an aircraft or satellite) of the temperature distribution of the snow and ice surface under study with the help of an IR radiometer (or of a map showing the isotherms based on the radiometer measurements). The IR radiometer proportionally transforms the changes in the temperature of the underlying surface into the changes in the amplitude of the electric signals at the radiometer outlet. IR surveys typically provide images of the surface which can be presented either in the form of a gray scale picture with areas of different contrast range, or in the form of a colored mosaic map.

LASER PROFILING OF ICE. A remote sensing method for recording the topography of the ice and snow surface along the flight line of an aircraft. Under the vertically stable atmospheric conditions that frequently occur in the Arctic, this method can determine the height of irregularities in the upper ice surface to within an accuracy of 10 cm.

MICROWAVE RADIOMETRY OF SNOW AND ICE SHEET. A remote sensing method for studying the structure and physical state of a snow and ice surface based on its emission of electromagnetic energy in the microwave portion of the electromagnetic spectrum. The microwave brightness temperature is also proportional to the thermodynamic temperature of the ice and snow and is a function of their thickness as well as other factors.

PHOTOGRAPHIC SURVEYS. Photographic surveys record data in the visible and near infrared intervals of the electromagnetic spectrum. One should distinguish between planned, prospecting, panoramic, and planned-prospecting photographic surveys.

RADAR SURVEYS. The determination of the thickness, structure and physical properties of ice sheets by the study of the electromagnetic radiation reflected and scattered by both interface surfaces between the ice and the surrounding media (air, water, rock, etc.) and also by scattering within the ice and snow. The analysis of the resulting radar images enables one to determine information such as the sizes and shapes of ice formations, the compactness of the ice, and areas of open water in and on the ice. Repeated surveys of the same area allows one to measure the deformation of the ice, as well as the speed and direction of the ice drift. Both microwave radiometry and radar share the distinct advantage that they are not limited by clouds or by darkness.

VISUAL STUDIES. Visual observations made with a naked eye from aboard an aircraft and the subsequent transference of the results of these observations onto a map with the help of a suitable symbolic notation.

RESIDUAL OR NON-ELASTIC DEFORMATION. See Ice Deformation; Plastic Deformation.

RESULTING ICE DRIFT. An estimated ice drift, the direction of which is defined by the vector linking the start and the end of drift, and the speed of drift by the ratio of the vector length to the drift time.

RIM. A strip of open water between an ice sheet and the shore formed prior to a river debacle. Rims result both from the partial ice movement away from the shore and the melting of ice associated with a rise in the water level of the river.

ROPACK Russ. A separate fragment of an ice-floe either standing vertically or sloping on a otherwise comparatively even surfaced ice sheet ( Photograph 51). Such features are presumably supported by the underlying ice sheet and usually have small, if any, underwater portions. Therefore they result in local departures from isostatic equilibrium. [There is no equivalent English expression.]

ROTATION OF FLOES. The rotation of floes around a vertical axis. Particularly strong rotations are observed along borders between fast and drifting ice.

ROUTE OF ICE DRIFT. A value equal to the length of a trajectory arc from the starting point of the drift calculation to the point where the ice-floe is located at a given moment.

RUNNING SPEED OF A VESSEL (CONVOY OF VESSELS) IN ICE. The average speed of a vessel’s motion (or of a convoy of similar vessels) as defined by the route distance with uniform ice conditions divided by the navigation time.

S

SALINITY OF SEA ICE. A parameter providing an estimate of the chemical composition of seawater based on the available sum of the ions of chlorine, bromine, fluorine, sulfate, bicarbonate, sodium, potassium, magnesium and calcium in the water. The measurement is usually made by determining the electrical conductivity and temperature of the solution and is expressed as parts per thousand (‰) [grams of "salt" per kilogram of solution]. Near surface salinities in the polar oceans are commonly in the range of 32–34 ‰ while sea ice salinities are commonly in the range of 3–10‰. Salinity determinations on sea ice are performed on completely melted samples.

SALTING OF ICE. The increase in the salinity of sea ice resulting from the infiltration of sea water into the surface layers of an ice sheet due to distortions in the isostatic balance (e.g. depressions of the surface of the ice sheet to below sea level as the result of loading by a heavy snow pack on the surface of the ice). Salting can also occur in the desalinated lower layers of the ice after the termination of the summer melt season.

SCALE EFFECTS ON ICE SAMPLE STRENGTH. This effect is the result of the dependence of the strength of an ice samples upon their size with smaller samples generally being stronger than larger samples.

V.V. Lavrov has suggested a formula which allows one to calculate the flexural strength s1 of an ice sample with given dimensions from the experimentally measured flexural strength s2 of the geometrically similar sample of the same material but with different dimensions:

where is the length of the ice sample and h is its thickness (h is approximately equal to width). In the case where samples are not geometrically similar, their moduli of deformation Edef1 and

Edef2 are not equal and the above formula can be recast in the following form:

Comparison of the calculated values with the results of experiments gives satisfactory agreement. When dimensions of samples change from 5 ´ 5 to 100 ´ 100 square centimeters, the difference between the calculated and measured values of flexural strength does not exceed 25%.SCATTERING OF ELASTIC ENERGY BY ICE. A measure of the internal friction y as defined as the relation between the energy scattered by an oscillating ice body during a single oscillation period to the maximum elastic energy of this body:

SCIENCE OF SEA ICE. A branch of knowledge which studies the formation, structure, composition, properties, evolution and destruction of sea ice as it occurs naturally in the world’s oceans. The science of sea ice is a branch of oceanography.SCIENTIFIC & OPERATIVE GROUP. A group of hydrometeorological profile experts possessing both high qualifications and extensive on-the-job experience, established for the period of ice navigation.SCIENTIFIC & OPERATIVE MAINTENANCE. Work implemented by hydrometeorological experts directed toward facilitating the reception of information about actual and forecast hydrometeorological and ice conditions and the transmission of this information to Arctic sea operation managers and to captains of ice-breakers and transportation vessels.SCOUR. An elongated hole, resulting from the local acceleration of currents, in river ice (often called a "pool") or in fast sea ice. SEA ICE COVERAGE. A parameter characterizing the distribution of ice in the sea (or a part of the sea) and defined as the ratio of the area covered with ice to the total area of the sea (or its part). Parameters such as compactness and age are not taken into account. The relative area of ice is expressed as a percentage.SECULAR BEHAVIOR OF ICE PARAMETERS. The natural changes in ice parameters observed over tens to hundreds of years. Typically these values are determined on the basis of data averaged over many years.SEISMOACOUSTIC MODULUS. See acoustic modulus (Young’s Modulus). SHEAR MODULUS (SHEAR RIGIDITY). The ratio of the shear stress t at some point of the body to the shear angle g, whose value determines determines the distortion of the initially right angle between the planes in which tangential forces are acting ( Figure 8): The modulus G characterizes the ability of ice to resist a change in its shape at constant volume. The shear modulus is smaller than Young’s modulus by a factor of 2.6 - 2.7. In the literature, authors sometimes use the terms distortion modulus or the modulus of transverse deformations instead of the term shear modulus.SHELF GLACIER. A floating or partially grounded glacier extending off-shore in the shape of a shelf which gradually thins toward its outer edge where it ultimately ends in an ice cliff ( Photograph 37). In the near-shore part (measuring away from the coast) the thickness of a shelf glacier changes from 1,300 m or more to 300 m and near its seaward edge from 400 m to 50 m where the ice cliff is called a glacier barrier. The glacier’s speed increases from 300-800 m/year near the coast to values up to 1,800 m/year near the ice edge. SHELF HARBOR. A bend in an ice barrier forming a bay where vessels can moor and unload directly upon the ice shelf.SHELF ICE. Stagnant ice of a shelf glacier that is floating. Such ice typically has thicknesses of 40-60 m. About 2/3 of its thickness from the bottom consists of saline ice, the upper one third of the ice is both fresh and layered with various inter-layers of mineral deposits. The upper ice surface is commonly wavy. The calving of arctic ice shelves results in the formation of ice islands.SHUGA (Russ.)See natural ice, intrawater ice. A type of new ice appearing as an accumulation of spongy white lumps a few centimeters across. Shuga can form from slush, grease ice and occasionally from anchor ice rising to the surface.SIZE DISTRIBUTION FUNCTION FOR ICE FLOES. A probabilistic measure taking into account the relative number of ice-floes in each size gradation. In practice, we often use the differential distribution function F(Si) - the ratio of the area comprised of ice-floes of size Si to the total area occupied by all the ice-floes. If the probabilities of ice-floe distribution by size are given discretely, then: where pi = pi (Si) is the frequency of ice-floes of a certain area Si and Sav is the average area covered with ice.SMALL-SCALE DRIFT OF ICE. The drift of ice at distance scales of from several meters to several kilometers and lasting from fractions of a second to tens of minutes.SNEZHURA. (Russ). A mixture of water and snow with no rigidity existing as a thin surface layer on the ocean or on the surface of an ice cover. Snezhura does not contain frazil crystals. [There is no equivalent English expression.]SNOW CONCRETE. A mixture of snow and water at a 4 : 1 or 3 : 1 ratio that is first compacted and then frozen.SNOW-COVERED ICE. Sea or fresh-water ice with various degrees of snow coverage.SNOW CRUST. A crust of fine-grained strongly bonded snow on the surface of a snow cover consisting of closely-packed snow particles compacted by wind. Snow crusts usually develops on windward slopes of packed snow drifts.SNOW-DRIFTS. Wind-drifted accumulations of snow which have been deposited on the lee sides of obstacles.SNOW RIDGES. Large snow-drifts that are elongated to the windward and that have lengths of up to several meters and heights of up to 1.5 meter (normally, 20 - 30 centimeters). The snow ridges alternate with wind furrows. In English these are often referred to as longitudinal snow dunes.SOUND VELOCITY IN ICE. The velocity of elastic perturbations (deviations of the water molecules from their equilibrium positions) that depends on the compressibility and the density of the ice. If not specified otherwise, the term "sound velocity" refers to the phase velocity of the propagation of elastic oscillations in ice. The speed with which the phase of a monochromatic infinite sinusoidal wave moves in space is defined as:

,

where T is the period, l is the wavelength, and is the wave phase. A constant phase moves at the velocity , (the phase velocity).

SPACE FACTOR OF A HUMMOCK. The ratio of the volume of the ice in a hummock (excluding the holes and air layers between the ice blocks forming the hummock) to the total volume of the hummock where the latter is defined on the basis of the external geometry of the hummock.

SPACE SURVEY. The investigation of snow and ice formations using satellite based instruments operating at various different spectral intervals.

This method is very promising for monitoring ice boundaries, ice movements and for studies related to ice navigation.

SPATIAL HETEROGENEITY OF AN ICE COVER. The spatial variability per unit area in the observed numerical values of an element or indicator of an ice sheet (e.g., the distribution of the horizontal dimensions of ice-floes, the ice thickness distribution).

SPATIAL STRUCTURE OF THE ICE SHEET. The spatial disposition of ice formations, their aggregates, and open water as conditioned by differences in interactions that depend on the nature of the forces affecting the ice sheet and changing with both short-term and seasonal rhythms. All this forms a series of mosaic combinations alternating in space.

ARCH STRUCTURES. A structure formed by a system of bow-shaped cracks and channels. Such structures are commonly observed in areas that are close to large straits, e.g. Fram Strait, Long Strait, Bering Strait, etc. ( Photograph 52)

DENDRITIC STRUCTURES. A spatial structure formed by systems of branched cracks, channels, and open water spaces that is typical of ice sheets during the autumn time period.

LAYERED STRUCTURES. An ice sheet structure formed by a system of parallel, linear oriented cracks, leads, and open water areas, or a system of narrow parallel zones of chaotic ice formations. Such features are typically observed during the winter. As a rule, the ice in the zones formed between such main fractures is so highly deformed and compacted that it can only be crossed with difficulty even by ice-breakers.

POLYGONAL STRUCTURES. The structure of an ice sheet formed by systems of crossing cracks, channels, and open water areas. Such structures typically occur in spring ice sheets and in near-barrier regions. The prevailing shapes of ice formations of this structure are rectangular and double-wedged ice blocks (see Photograph 31).

SHEAF STRUCTURES. A structure formed by a system of one-sided directed cracks, channels, and fractures. Such structures are typical of locations where protruding capes or islands are observed (e.g. regions of the Cape of Desire, Rudolf Island). Trapezoidal blocks of ice are typically formed.

SPOTTED STRUCTURES. The spatial structure of an ice sheet where various combinations of ice fields, ice fragments and broken ice-floes form spots of either increased or decreased compactness. Spotted structures are typical of ice sheets in the summer.

VORTEX STRUCTURES. The spatial structure formed by ice sheet elements involved in cyclonic and anticyclonic vortices. It may occur in the form of ice spirals.

SPECIALIZED FORECASTS. Recommendations published by operative bodies of Roshydromet (Russian Hydrometeorological Service) based on the analysis and forecast of hydrometeorological conditions and designed to support the implementation of specific production tasks of separate industries in the national economy.

SPECIALIZED HYDROLOGICAL FORECASTS FOR NAVIGATION. Recommendations that include information about the most advantageous shipping routes in seas and oceans, or forecasts of the expected start and the end of transit periods by non-self-propelled vessels (lighters or barges).

SPECIALIZED ICE FORECASTS. Ice forecasts that contain information about the expected types of navigation conditions occurring on different sections of a route, the length of ice zones of varying age and compactness, and the estimated navigation times and charges for specific convoys along different routes.

SPECIALIZED FORECASTS FOR THE FISHING INDUSTRY. Recommendations that contain information about the estimated location of marketable schools of fish and the expected time for the start of the fishing season.

SPECIALIZED FORECASTS FOR ON-ICE TRANSPORT. Recommendations for the use of specific types of transport on ice roads depending on their bearing capacity.

SPECIFIC HEAT OF ICE MELTING. The amount of heat required to change a unit mass of ice which is at the melting temperature from the solid state into the liquid state.

At 0°C and normal atmospheric pressure the specific heat for clear bubble-free ice is 333.5 kJ/kg. This value is identical with the specific crystallization heat of fresh water.

For sea ice, the term effective heat of melting is used which is the heat needed to melt a unit mass of sea ice. The effective heat of melting of sea ice is appreciably less than that of pure ice as the result of its higher salinity.

SPECIFIC HEAT OF ICE SUBLIMATION. The amount of heat needed to cause a unit mass of ice to transfer into the vapor phase at the same temperature.

SPECIFIC HEAT OF WATER VAPOR SUBLIMATION. The amount of heat needed to cause a unit mass of water vapor to change into ice at the same temperature.

SPREAD OF AN ICE EVENT. The process of enlarging a sea ice sheet or area, or the area where an ice formation event occurs.

NON-ZONAL SPREADING. The spreading of an ice event or process without a correlation with a specific zonal feature (circle of latitude) in a given ocean area. It is one of the major physical and geographic mechanisms. For example, the spreading of ice in the Greenland Sea is of this type.

ZONAL SPREADING. The spreading of an ice event or process in the sea when the speed and direction of the event or process is essentially the same at all the points along a circle of latitude.

MAXIMUM SPREADING. The lowest latitude reached at maximum ice extent. For example, the location of the maximum winter border of sea ice in the world’s oceans is identified by two characteristics: the critical depth of the vertical convective circulation in the upper ocean and the conditional maximum depth of convective cooling as the result of the heat exchange between the ocean and the atmosphere at that site.

STABLE ICE FLOWS. The movement of ice in a single-direction during an extended time period. An example of such a drift system is the transarctic drift of ice from the seas of the Siberian shelf towards Fram Strait . This is well reflected on charts showing ice drifts in the Arctic Basin averaged for annual and even winter time periods. However, for shorter averaging periods and particularly during the summer season, ice drift in any direction may be observed in the same region.

STABILITY OF THE ICE DRIFT DIRECTION. The degree to which the direction of the ice drift system is preserved. Its value is determined by the ratio of the vector modulus of the average speed W to the average scalar speed W*.

.

The values of q change from 0 to 1. The more stable the ice drift, the closer to 1 is the stability coefficient. Ice drift may be considered to be stable at q > 0.85, and unstable at q < 0.60.

STAGNANT SEA ICE. A field of sea ice that remains relatively fixed in position as the result of the fact that it is frozen to the shore, ice wall, ice barrier, or shoal.

FAST ICE. Sea ice fixed to the shore by an ice wall or an ice barrier that is subject to small vertical tidal fluctuations as well as to minor horizontal displacements. Fast ice forms either as the result of the natural extension of an ice sheet out from the coast or by the freezing of a region of pack ice to the shore. In some regions in the Arctic a fast ice area may remain stable for two and more years while transforming from winter ice into old ice; and in Antarctic seas - into shelf ice. The width of fast ice may vary from a few tens of meters to several hundred kilometers (Photograph 11 and 53).

Fast Ice Foot. A narrow zone of fast ice that is fixed to the shore and is not affected by tidal fluctuations. This ice typically remains in place for some time after the fast ice breaks up.

Stable Fast Ice. The part of the fast ice located between the ice foot and the ice barrier, hummock, or a chain of hummocks grounded on a shoal (stamukhi).

Submerged Off-Shore Ice. The initial formation stage of fast ice represented by a strip of stagnant thin ice 200 m wide and frozen to the shore.

Unstable Fast Ice. An area of fast ice formed offshore of the hummock barrier and subject to fracturing and conversion into pack ice during any season of the year.

COASTAL RIDGE (OFF-SHORE ICE BAR). An ice pile occurring on a gently sloping shore.

GROUNDED ICE FLOE. A level ice floe or a slightly hummocky ice floe which has temporarily become shoaled.

ON-SHORE ICE. Small, broken ice-floes or ice-blocks found on the shore during periods of low tide or when pushed onto the shore by strong, on-shore movements of the offshore pack ice.

SHOALED ICE. An ice formation that has temporarily become stagnant due to its running aground.

STAMUKHA Russ. (Grounded Hummock). A large hummocky pile of ice grounded in water depths of 20 meters or more. The height of such stranded ice can be 10 m or more. The average void volume of such stranded ice is 0.35. Chains of stamukhi often form along coastal shoals (Photographs 53, 54).

STATE OF ICE SHEET. A set of qualitative and quantitative changes in ice sheet features and events occurring between two consequent surveys (observations) of the ice conditions in the same region. The two states of an ice sheet will be considered different if the numerical values of at least one parameter or indicator significantly differ from each other.

SPREADING ICE. The initial stage of ice rarefaction (picture 33).

BROKEN ICE. An ice sheet that is in a state of mechanical destruction; i.e., external forces have broken it into fragments of different sizes. One possible measuring unit for breakage during the winter will be the scale of the distances between cracks and leads and in the summer, the relative number of ice fields, fragments and broken ice. When estimating the degree of breakage of an ice sheet, one should note the direction and width of cracks, leads, and open water areas (rasvodije) and the age of the ice that has formed these features.

RAREFIED ICE. The ice that is in a state of rarefaction with the distances between the ice-floes increasing. The compactness of an ice sheet is measured using a 10 point compactness scale.

DESTRUCTING ICE. An ice sheet that is in a state of thermal destruction as the result of processes associated with melting.

Dried Ice. The ice after the surface melt water has flowed into the sea through cracks and the formation of thaw holes.

Lacy Ice. Ice on the surface of old floes which has been so completely dissected by melt processes that it now resembles lace.

Rotten (honey-comb) Ice. The ice in the final stages of melting that is friable and saturated with water. It has a dark-gray color and looks like a honey-comb ( Photograph 55).

Submerged Ice. Ice covered with a continuous layer of melt or river water.

COMPACT ICE. The ice which is in a state of compactness as indicated by a decrease in the distances between the ice-floes.

PRESSED or PRESSURED ICE. Ice which is under compression.

STATIC ELASTIC CHARACTERISTICS. Elastic characteristics defined in accordance with the results of tests performed without the observance of the conditions of elastic behavior in ice, e.g. by the relatively slow bending of beams and consoles. As a rule, elastic characteristics as determined by using static methods show a significant spread in their measured values that may differ from the dynamic characteristics by an order of magnitude or more.

The results of rapidly performed static tests made to define the elastic modulus are sometimes called the conditionally-instant, or quasi-elastic modulus.

STRENGTH CHARACTERISTICS OF ICE. The values that characterize the strength of ice as a solid.

Characteristics determined from sample loading times that do not exceed several seconds (from the start of the loading to the moment of failure) are called short-term (conditionally instant) strength. (see also Brittle strength).

PROPORTIONALITY LIMIT sH. The stress at which the deviations from a linear dependency between stress and strain reach the value as established by technical considerations. The criterion sH describes the adequacy of Hook’s Law in fitting a given set of data. In practical calculations sH= syield is taken as the basis ( Figure 12).

STRENGTH LIMIT (TEMPORARY RESISTANCE) OF ICE sbr . The conditional stress (defined by the ratio of the effective force to the initial cross-sectional area of the ice sample), corresponding to the peak load preceding the failure of the sample. It is the primary characteristic of materials that fail at low plastic deformations.

The scientific and technical literature includes the following terms for this class of failure: tensile (fracture), flexural, compressive (under either uniaxial or complex loading) and shear strengths.

When evaluating these types of characteristics, the total time of loading should rarely exceed a few seconds from the start of loading to the moment of destruction. Because of this reason these characteristics are also referred to as the conditionally-instant or brittle short term strengths or the ultimate strengths under tensile, bending, compressive and shear stresses.

Limits of the Tensile and Flexural Strength of Ice st and sf. Mechanical characteristics determined through experiments in which ice samples are subjected to critical tensile and flexural deformations.

In accordance with recently agreed international recommendations, the following optimum methods should be used to determine ice strengths. To obtain the tensile strength st, dumb-bell shaped samples whose dimensions of the cross-sections where the fracture occurs significantly exceed the sizes of the ice crystals in the sample, should be used. If the bending or flexural strength sf is required, then floating cantilever beams that are cut using the entire thickness of the ice sheet should be used to establish the failure moments.

These calculations are performed using the following formulae:

where Pt and Pf are the loads at failure, St is the cross-sectional area at the location of the fracture, is the length of cantilever, b is the cantilever width, and h is the ice sheet thickness.

There are a number of empirical dependencies relating st and sf to factors such as the temperature and the salinity of the ice, the loading rate, the specific structural features of the sample, and its geometric dimensions.

It is important to note that when ice fails in flexure (bending), as in the case of a fixed cantilever whose free end is pulled upward, the sample is subjected to a complex set of stresses: i.e., the upper portion of the sample is subjected to compression while the lower portion of the sample is subjected to tensile stresses. As a result st is, on the average, 30%-40% lower than sf.

Limits of the Compressive and Shear Strength of Ice. and . Mechanical characteristics determined through experiments in which ice samples are subjected to critical compressive and shearing deformations.

The compression strength of ice scom is obtained by axially loading either prismatic or cylindrical samples to failure. In performing such tests, great care should be taken to assure that a plane uniform stress state is achieved in the portion of the sample that fails. This is usually achieved by minimizing the tangential stresses (perpendicular to the axial load) at the places where the ends of the sample contacts the loading platens.

Here Scom is the cross-sectional area of the sample as measured perpendicular to the direction of loading and Pcom is the compressive stress at failure

The shear strength of ice is calculated using:

where Psh is the destructive load directed along the area of shear Ssh.

It has been determined that scom increases with decreasing temperature. Also its values when the load is applied perpendicular to the direction of crystal growth (typically in the vertical) are larger than when the ice is loaded perpendicular to that direction (parallel to the surface of the ice sheet). Shear strengths are smaller if the plane of shear is perpendicular to the long axes of the crystals.

LIMIT OF YIELD sy. The stress that corresponds to the lower position of the yield platform as shown in Figure 12. In ice, such a platform is observed at moderate deformation rates when testing using uniaxial compression. Physically it corresponds with the start of internal crack formation. In general, the yield limit fixes the boundary between the elastic and elastic-plastic zones of deformation and is the major characteristic of the strength behavior of plastic materials.

LIMIT OF ELASTICITY sel. The stress at which the residual deformation initially reaches a value that is arbitrarily fixed by technical considerations (e.g. 0.001; 0.003; 0.03%). This criterion limits the region where Hooke’s law is assumed to hold. In practical calculations, sel= sy is usually assumed (see Figure 12).

STRUCTURE OF AN ICE DRIFT FIELD. The aggregate of interrelated elements that characterize the spatial changes in an ice drift field. These elements include stable ice floes as well as their rotations, vortices, and spirals.

STUCK ICE. Ice formed through atmospheric icing that grows on the surface of a project due to the freezing of either frazil crystals or snow mixed with sea water.

STUFFED ICE. A condensed mass of primary or young ice fragments formed as a strip in coastal regions, shoals, and close to fast ice due to the strong effect of wave motion. The vertical thickness of stuffed ice can reach 20 m or more.

SUBLIMATION OF ICE (SNOW). The direct transition of ice (snow) from the solid to the vapor phase.

SUBSIDENT ICE. An area of an ice sheet in a shoal close to the shore that has subsided due to a decrease in the local water level.

SURFACE BRINE. A concentrated salt solution formed on the surface of an ice sheet during fast ice formation.

SUPPORTING POWER (BEARING CAPACITY) OF AN ICE SHEET. The ability of an ice sheet to support a variety of different loads without failing or undergoing undue damage.

The supporting power of an ice sheet is usually expressed in terms of the maximum load that can be supported by the sheet for a specified period of time without resulting in the failure of the sheet. The supporting power of an ice sheet is significantly affected by both the length of time that the load is applied and how the load is distributed. Generally, three typical ice loading regimes are distinguished:

1) dynamic, when the stresses vary widely but within the elastic range;

2) static, when the inertia forces may be ignored;

3) durable load regime, when the plastic properties of ice are fully utilized.

For many types of logistical tasks, the loading is only applied for a short period of time and the stresses always remain less than the elastic limit. In such cases an ice sheet can be considered to be an elastic plate resting on an elastic foundation. Clearly the bearing capacity of a specific ice sheet should be less than the loading that would result in the occurrence of cracks that completely penetrate the ice sheet, in that such cracks are known to significantly decrease the bearing capacity. The supporting power of an undamaged ice sheet at locations near an open lead is also significantly reduced.

The analysis of ice sheet behavior based on elastic plate theory permits only an approximate analytical description of the behavior of the ice under loading, especially under loads of long duration. In such cases an accurate calculation of the maximum stress considering creep and an estimate of the influence of cracks on the load capacity of the ice should be included as should the effects of the vertical temperature gradient across the thickness of the ice.

SWELLING HILLS. Small mounds of ice with heights of several dozen centimeters caused by the volume expansion which accompanies the freezing of water lenses located in water pools that were deeply thawed ( Photograph 56). These features primarily occur in old ice.

SYSTEMS OF UNIFORMITY VIOLATIONS. The spatial distribution of sets of cracks, leads, and open water areas (rasvodije) in a certain area of ice at a specific moment of time. Straight, crossing, arcuate, branching, as well as other fracture systems can be distinguished.

T

TANGENT OF THE MECHANICAL LOSSES IN ICE. A mechanical characteristic of ice that is a measure of its internal friction:

tan j = Q-1,

where corresponds to the displacement between the stress and the deformation as determined using quasi-elastic vibrations with a frequency ; and is the reciprocal of the mechanical quality factor (by analogy with the Q-factor of an oscillatory electric circuit).

TEMPORARY RESISTANCE. See strength characteristics of ice.

THAWED PATCH. A vertical hole where an ice floe has melted completely through during the summer thaw period.

THEORETICAL ICE STRENGTH. A hypothetical property of ice scalc that is calculated by assuming that the strength of a failure surface is given by the simultaneous breakage of all interatomic linkages located on the surface. As with other solids scalc for ice is estimated by the value 0.1 E, where E is Young’s modulus.

Actual strength values are usually several orders of magnitude lower than the theoretical values. The reason for low strengths of real materials is the uneven distribution of internal stresses causing the interatomic linkages to be loaded unequally. Also real materials invariably contain flaws (dislocations) which appreciably lower their strength.

When both external and internal stresses are considered, local deformations may occur that may reach the theoretical strength values, leading to breaks in the interatomic linkages The growth and linking of such failures form microscopic cracks whose development results in the destruction of the body. The theoretical strength is also called the ideal strength or the cohesion force density (i.e. the force of molecular interaction of parts of the same body) or simply cohesion, that may be characterized by the heat of evaporation.

THERMAL CONDUCTIVITY OF ICE (THERMAL CONDUCTIVITY COEFFICIENT). A parameter l characterizing the effectiveness of thermal energy transfer in ice. The thermal conductivity is the proportionality coefficient between the thermal flux density q and temperature gradient as given by the well-known equation:

q = –l grad T

Strictly speaking, the thermal conductivity of ice is numerically equal to the thermal flux density observed at a temperature difference of 1°K per unit distance. If the temperature decreases, the thermal conductivity increases. In accordance with theoretical calculations and laboratory measurements, the thermal conductivity of freshwater ice is equal to 2.22 W/(m ( K) at a temperature of 0°C.

THERMAL DIFFUSIVITY OF ICE. A parameter characterizing the rate of change of the ice temperature during non-stationary thermal processes. The coefficient of thermal diffusivity a is given by

,

where Cp is the specific heat of ice at constant pressure, is ice density and . is the thermal conductivity.

THERMODYNAMICAL MODELS. Models describing processes of growth and melting of sea ice in terms of sets of equations based on the thermal conductivity and the heat balance equations.

THERMOPHYSICAL (THERMIC) PROPERTIES OF ICE. Ice properties that define the conditions of heat transfer and ice temperature change.

THERMIC DESTRUCTION. Destruction of an ice sheet as a result of its melting usually resulting from increases in the air temperature to values above 0°C. Thermic destruction decreases ice strength, changes its structure and texture, and diminishes the horizontal and vertical dimensions of floes, etc.

External evidence of thermic destruction is the breaking and splitting of ice sheets as fixed by the following times: the day when part of fast ice splits off; the day when the first signs of melting and decreasing strength occur; the day when the visible area of fast ice (excluding its bottom) is dissected by a great number of cracks resulting from horizontal shifts in the ice but not resulting in a measurable decrease in compactness; and finally the day when the fast ice has broken into ice blocks that have shifted in relation to each other, appreciably decreasing the compactness of the ice.

THERMAL CRACKING OF ICEBERGS. A process of thermal iceberg destruction resulting from the release of the energy contained in the compressed air contained in the bubbles in the ice. The pressure in such bubbles ranges from 0.5 to 2.0 MPa. The air released from such bubbles may cause cavitation or resonance excitation.

TIDAL ICE DRIFT. Ice drift resulting from or affected by tidal currents. Depending on the character of the tides, the drift may be semi-diurnal or diurnal.

TIME OF SAFE LOAD PARKING ON ICE. The period between the time when a known load is placed on an ice sheet and the time when the ice sheet starts to fail under the load (i.e. when there is a loss of bearing capacity).

Based on the experimentally determined observations of breaking loads, one can derive the following expression for calculating the time tp that a load may safely remain on an ice sheet:

.

Here Pp(0) is the load causing plate to fail immediately after its application, i.e. at time

tp = 0; Pp(tp) is the load causing the ice plate to fail after time tp where time is expressed in hours. At tp > 0, Pp(tp) < Pp(0).

It is important that one correctly determine the value of Pp(0). Probably, the most accurate results to date have been obtained by D.F. Panfilov. In his experiments on fresh water ice the static load was created with the help of a die (stamp) and parameters were chosen so as to result in failure within a 5 - 20 second interval. By using averaged experimental data, one can construct a curve, which is characterized by a small scatter of points and which can be approximated by the following equation:

where b is the diameter of the loading area ; is the so-called action radius given by where is the flexural rigidity of a plate and r is the density of the water.

For technical applications one must also know the loads under which an object can park on the ice or move slowly over its surface without failure occurring. One must also know the loads which will cause the ice to fail instantly (values useful in designing icebreakers). These loads correspond to the upper (U) and lower (L) envelopes limiting the experimental data. The area under the lower curve delimits permissible loads while that area above the upper curve corresponds to failure loads. These curves can be described with the help of the following formulas:

Therefore, in accordance with the results obtained by Panfilov, a permissible load for an unbounded ice plate at –10°C when the load is concentrated at b< h can be determined as follows

Here can be considered to be equal to the value of the flexural strength of a floating cantilever beam.

According to Panfilov’s results, the permissible load applied to the edges of a lengthy crack in an ice sheet (e.g., in the case of a bridge between two semi-infinite plates) can be determined from the condition

For a semi-infinite plate the permissible load is given by

Panfilov’s experiments were performed at . He also showed that (Pp)L 2Pcr, i.e., that cracks in ice develop at loading values equal to half the load corresponding to the lower limit as described above.

TIME RESISTANCE. See strength characteristics of ice; ultimate strength.

TORTUOSITY COEFFICIENT OF ICE CRYSTAL FACES. A parameter that characterizes the degree of tortuosity (twisting or crookedness) of ice crystal faces as compared to an ideal crystal. The coefficient of tortuosity characterizes the degree of ice crystal ideomorphism (a term applied to crystals bounded by their own rational crystal faces).

TORTUOSITY OF ICE DRIFT. Frequent changes in the direction of ice drift with time result in tortuous drift trajectories. The degree of tortuousity is measured in terms of the tortuousity index which is defined by the ratio of the actual length of ice-floe drift track, including all turns, to the displacement of an ice-floe during a specified period of time ( Figure 16). For instance, a daily tortuosity index is equal to the ratio of the sum of the absolute values of the drift rate measured every hour, to the great circle distance between the starting and ending points.

TOTAL ICEBERG DISCHARGE. The mass of fresh continental ice discharged into the sea from some specified location.

For example, for the Northern hemisphere, the total iceberg discharge is approximately 4.7´1017 g/year. Of this value the Greenland icecap contributes 4.6´1017 g/year; Spitsbergen archipelago - 0.95´1017 g/year; Franz Josef Land - 0.026´1017 g/year; Novaya Zemlya - 0.02´1017 g/year; and all the other arctic islands - 0.004´10 17 g/year;

TROUGHS. This term refers to furrows (also referred to as gouges) on the sea floor caused by the ploughing action of grounded icebergs. Troughs may occur at depths of up to 380 m. At the present, extreme dimensions of furrows are known to be up to 3 km long, 30 m wide and 6.5 m deep.

TYNDALL FIGURES (FLOWERS). Melt figures that occur inside ice crystals produced by internal melting resulting from absorbed radiant energy. Tyndall figures are located parallel to each other in the basal planes and resemble snowflakes in their shape. X-ray studies have shown that the directions of the arms of the figures indicate the directions of the a crystallographic axes. The figures are named after John Tyndall who first described them in 1858.

TYPE OF ICE. A taxonomic subdivision of ice classification used as an addition to generic types of ice. Types of ice include classifications by structure, composition, dimensions, an genetic origin, etc.

U

ULTRASONIC MODULUS. See acoustic modulus of ice elasticity (Young’s modulus).

UNDERHUMMOCK. The underwater part of a hummock whose draft usually, depending on its age, exceeds the hummock’s above water height by 3.5 to 5 times. If the ice feature is a hummocky ridge, its underwater portion would be commonly be referred to in English as a ridge keel.

UNDERWATER ICE DOME. A concavity in the ceiling (lower surface) of old ice. Underwater ice domes serve as traps for fresh melt water that flows under the ice in the spring and in the summer as well as for potential gas accumulations, oil products and other substances spilled under the ice and having a lower density than sea water. [In the non-Russian submarine community, these features are called skylights.

V

VELOCITY OF WAVE FRONT. See group velocity of wave spreading in the ice sheet.

VERIFICATION OF FORECASTS. The assessment of reliability or validity of a set of forecasts.

VESSEL (CONVOY) DRIFT. The passive movement of a vessel (convoy) under the influence of wind and currents. In cases where the drifting vessel (convoy) is beset, the movement is the same as the surrounding drifting ice.

VESSEL ICING. The formation of an ice layer on the body of a vessel or on its main deck and superstructure due to the freezing of water or spray ( Photograph 44). Vessel icing is observed when the vessel moves through open water at air temperatures below 0°C.

VESSEL MOVEMENT BY RECIPROCATING MOTION. Reciprocating motion of a ship with stops due to complicated ice conditions followed by acceleration and the breaking of ice. In English this procedure is called backing and ramming.

VISCOUS ICE FLOW. During certain types of loading situations the deformation of ice can be well described as behaving in a viscous manner; i.e., as a Newtonian viscous fluid which is a material whose strain rate is linearly proportional to stress :

In the above relation A is a yield coefficient which is a function of temperature, of grain size, and of parameters associated with diffusive processes in ice crystals. The coefficient is numerically equal to the reciprocal of the viscosity coefficient. The variations in A that are observed when investigating subjects such as glacier flow are the result of the increase in stresses with time and of the fact that ice properties deviate from those a perfectly viscous fluid. The terms "viscous or quasiviscous ice flow" are best applied to ice at near melting temperatures when deformation occurs as the result of small loads. It is known that creep processes in sea ice are facilitated by the fact that it contains liquid brine.

VOLUME MODULUS OF ELASTICITY. See Ice Compressibility.

W

WAKE BEHIND AN ICEBERG. A band of freshened and cooled water occurring behind a drifting iceberg. The influence of an iceberg on the temperature and the salt content of nearby sea water depends on the dimensions of the iceberg as well as its rate of melting.

WATER ICE. See hydrogenic, or congelation ice

"WATER" SHADOW. An area of open water located on the leeward side of an individual iceberg located among pack ice. "Water" shadows of many large-sized icebergs can merge into ice-free water areas that extend for up to dozens of kilometers.

WATER SKY. A comparatively dark sky observed near the horizon over areas of open water located in a region of unbroken ice.

WAVY ICE. An area of young ice (sometimes one-year thin ice) with a wavy surface that has resulted from prolonged compression ( Photograph 15). This ice feature is characteristically observed in recently refrozen leads, channels and polynyas. In some places in the Antarctic the horizontal stresses necessary to buckle such thin ice sheets are provided by the movements of near-by glaciers and icebergs.

WAVES IN THE ICE. The occurrence of periodic deflections in an ice sheet (or an ice sample of limited size). The statistical characteristics of these oscillations (amplitude, wavelength, period, velocity) depend on the visco-elastic characteristics of the ice (density, elasticity modulus, bulk modulus, coefficient of mechanical losses) for mechanical processes and on the electric characteristics of ice (dielectric constant, loss tangent, refractive index) for situations where the propagation of electromagnetic waves in ice are being considered.

AIR-COUPLED FLEXURAL WAVES. Waves originated by the interaction between flexural waves propagating in the ice and sound waves propagating in the air, under the condition that the two velocities are equal.

ELASTIC WAVES. Periodic mechanical deformations, the propagation of which in ice causes sign-variable mechanical stresses having amplitudes that do not exceed the elasticity limits of the ice.

FLEXURAL-GRAVITATIONAL WAVES. A wave process in ice fields caused by elastic forces in the ice field (considered as an elastic plate) and by gravitation. Frequencies of flexural-gravitational waves vary between 0.1 and 10 Hz depending on the ice thickness while the average wave amplitude ranges between 200 - 250 micrometers.

Flexural-gravitational waves can cause breaking of the edges of an ice sheet even during the winter. This process is particularly striking in the Southern Ocean.

GRAVITATIONAL WAVES. A wave-like motion of an ice sheet caused by the propagation of gravitational water waves (surface and internal) ( Photograph 57). In the Arctic and Antarctic, the gravitational waves observed in the ice are the result of storms in the open ocean. The period of gravitational waves ranges between 5 to 200 s for wind-excited waves and 3 - 30 minutes for slow waves [15].

LONGITUDINAL WAVE (VOLUME WAVE OR EXPANSION WAVE). A wave that propagates in ice with a velocity given by

where E is Young’s modulus, n is Poisson’s ratio and r is the ice density. This type of wave is connected with changes in the ice volume (compression or expansion).

In longitudinal waves, the particles are displaced parallel to the direction of wave propagation. The velocity of longitudinal waves in a sheet of sea ice depends on the ice density and ranges from the velocity of sound in snow to the velocity of sound in water.

RALEIGH WAVES. Elastic surface vibrations propagating along either free or lightly-loaded boundaries in ice. Their amplitude drops off rapidly with depth into the ice sheet. The velocity of Raleigh waves is determined by the formula:

where n is Poisson’s ratio and is the velocity of propagation of the transverse wave.

SLOW WAVES. The waves that develop in an ice sheet when it is subjected to the impact of short-period ocean internal waves [15]. Observed periods range from 3 to 30 minutes for ice up to 10 m thick. The phase velocity of slow waves varies from 0.5 to 2.0 meters per second.

TRANSVERSE WAVES (DISTORTIONAL WAVES). A wave that propagates in ice with a velocity Ct without causing a change in volume. In transverse waves, points are displaced in the direction perpendicular to the direction of wave propagation. The velocity of a transverse wave can be calculated using

where G is the shear modulus and r is the ice density.

The expressions for velocities of longitudinal and transverse waves are valid for an unbounded continuous isotropic medium whose dimensions in all directions are significantly larger than the wavelength.

WIND DRIVEN DRIFT OF ICE. The drift of ice under the effect of wind.

WIND FURROWS. A deflation form of snow surface relief caused by wind erosion of dense snow. They occur as elongated furrows located between wind-weathered ridges of snow (sastrugi) ( Photograph 58).

X

Y

YOUNG ICE See landfast ice

Z

ZONE OF ISLAND INFLUENCE ON ICE DRIFT. The area around an island where the island’s presence decreases the drift rate of pack ice and distorts its direction.