Glossary_4

RUSSIAN GLOSSARY OF SEA ICE TERMINOLOGY

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Glossary Terms: A-D, I, S-Z

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 s r ( 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 s¥ (see Figure 7) at which the deformation does not change ( ). At stresses s <s¥ , the ice does not fail. At s > s1 ( t << t1) 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" sbr may be applied, which is sometimes called the brittle strength of ice.

LIMIT OF LONG-TERM ICE STRENGTH OR CREEP LIMIT. The conditional stress s s, 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 sxx , syy , szz , txy = tyx , tyz = tzy , tzx = txz 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 sij , 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 micro-relief.

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.

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

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.

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 normal stress s to the relative bulk compression D which is given by D = exx + eyy + ezz .

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 s* = E eo between the amplitude of a periodic stress s(t) = so exp (iwt) oscillating at frequency w and its strain component e(t) = eo exp (iwt)

The tangent of the angle j 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 t = Ö te ts and E = Ö EREn we get

where the difference

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

DYNAMIC MODULUS OF ELASTICITY E(w) 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:

where te is time of stress relaxation at constant strain and ts 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 s = f(e) 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 s = f(e) (see the diagram in Figure 14) at the origin of the coordinate frame [ds/de]e = 0. 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-axis 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 1/3 tom 1/2.

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

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.

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).

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 its 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 exx , eyy , ezz are deformations along the corresponding axes.

For isotropic ice nxy = nyz = nzx = n. For an ice monocrystal the properties are anisotropic and nxy ¹ nyz ¹ nzx . 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 42).

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

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-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.

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

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 trf strongly depends on the microscopic characteristics of ice and, in particular, on mean parameters that characterize interactions between particles: the time tc 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 trf >> tc . Fast processes include dielectric relaxation, elastic and spin-lattice relaxation.

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

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 Maxwell’s model of a solid body, the relaxation time of stresses in ice is a function of viscosity h 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 . 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 Russian term for remote sensing occurs in many Russian translations.]

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.

RESIDUAL OR NON-ELASTIC DEFORMATION. See Ice 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.

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Glossary Terms: A-D, I, S-Z