Glossary_3

RUSSIAN GLOSSARY OF SEA ICE TERMINOLOGY

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Glossary Terms: A-D, E-H, J-R, S-Z

I

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 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 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 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 CLASSIFFICATION

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 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.

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]. In the following table Number refers to the number of icebergs per 1000 km2 and average distance between icebergs is given in , km.

Points | Number | Average Distance
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

ICEBERG DEPOSITS. Moraine 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 an 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 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).

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.

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 this classification 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.

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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 mono-crystal 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 depend 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 = s1, 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. At s = s2, 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 s¥ (called by K. F. Voitkovskii the limit of long-term creep), the deformation shall continuously increase at a constant rate. The s¥ value is characterized by the fact that if s > s¥ the ice creep is accompanied by a formation of micro-cracks, 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 di-trigonal-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 x 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.

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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 have 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 from 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 eP . The components of this tensor [provided that elastic deformation eE is small compared to the plastic deformation (i.e., that e = eE + eP . » eP .)] are not simply connected with the components of stress tensor s. As long as eP is not a function of state, there are no ice plasticity characteristics connecting eP and s that could be considered as constants similar to the elasticity constants that connect the elastic deformation tensor eE and s.

The speed of plastic deformation eP depends on instantaneous s values, temperature T, and the ice structure. When there is a linear connection eP(s ) 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.

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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 17). 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.

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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 th on the "failure area" depends on the normal pressure sh acting on this area, i.e., th = f (sh ) , then on the plane th , sh 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

t n = F + s n tan j

and using the experimental dependence th = f (sh ) ( Figure 11), represented by an envelope of Mohr circles (e.g. constructed with the help of principal stresses measured for a non-uniform triaxial compression at s1 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 j, 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 j and F are not constant. As the stress grows, the value of th 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 TRANSFER BY CURRENTS. Ice drift caused by the effects of either permanent or transient ocean currents.

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 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 { h = ( tS - tE ) / }.

ICE VISCOSITY INDEX (INTERNAL FRICTION COEFFICIENT). The coefficient of ice viscosity h 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 tshear 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 h 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, h 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 ¶je 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 ¶js 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 c 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 ¶jc 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 2pf where

and w is the angular velocity of the Earth’s rotation, and j 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 both the 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 the 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.

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Glossary Terms: A-D, E-H, J-R, S-Z