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(1) combined processes (such as sublimation, fusion or melting, evaporation) which remove snow or ice from the surface of a glacier or from a snow-field; also used to express the quantity lost by these processes (2) reduction of the water equivalent of a snow cover by melting, evaporation, wind and avalanches.

the area of a glacier where more glacier mass is lost than gained.

depressions in the snow surface caused by the sun or warm, gusty wind.

mound or layer of moraine in the ablation zone of a glacier; the rock has been plucked from the mountainside by the moving glacier and is melting out on the ice surface.

period during which glaciers lose more mass than they gain; usually coincides with summer.

area or zone of a glacier where snow and ice ablation exceed accumulation.

(1) the ratio of the mass of water vapor to the volume occupied by a mixture of water vapor and dry air (2) mass of water contained in a unit volume of moist air.

growth of a cloud or precipitation particle by the collision and union of a frozen particle (ice crystal or snowflake) with a super-cooled liquid droplet which freezes on impact.

all processes by which snow or ice are added to a glacier, this is typically the accumulation of snow, which is slowly transformed into ice; other accumulation processes can include avalanches, wind-deposited snow, and the freezing of rain within the snow pack.

area of a glacier where more mass is gained than lost.

period during which a glacier gains more mass than it loses; usually coincides with winter.

area of a glacier where more mass is gained than lost.

the extent to which the readings of an instrument approach the true value of the calculated or measured quantities, supposing that all possible corrections are applied.

rain or snow containing acidic substances, resulting from the atmospheric pollution mainly with sulfur and nitrogen; acid precipitation has a lower pH than unpolluted rain.

a foundation pile on which a cold air refrigeration system has been installed to remove heat from the ground.

special design and construction methods used for engineering works in permafrost areas where permafrost degradation cannot be prevented.

an ice wedge that is growing as a result of repeated (but not necessarily annual) winter cracking.

the layer of ground that is subject to annual thawing and freezing in areas underlain by permafrost; also known as seasonal frost.

a foundation pile on which a liquid coolant refrigeration system has been installed to remove heat from the ground.

a mass of rock fragments and finer material, on a slope, that contains either an ice core or interstitial ice, and shows evidence of present movement.

the process by which characteristic landforms are currently developing as a result of thawing of ice-rich permafrost or melting of massive ice.

a general term referring to several forms of slope failures or failure mechanisms commonly occurring in the active layer overlying permafrost.

the thickness of the layer of the ground that is subject to annual thawing and freeing in areas underlain by permafrost.

the tensile or shear strength which has to be overcome to separate two objects that are bonded together by ice.

the process by which two objects are bonded together by ice formed between them.

when a mountain glacier's terminus extends farther downvalley than before; glacial advance occurs when a glacier flows downvalley faster than the rate of ablation at its terminus.

the horizontal transfer of air mass properties by the velocity field of the atmosphere.

fog which forms in the lower part of a warm moist air mass moving over a colder surface (land or water).

non-gaseous substances, divided into solid particles or liquid droplets, held in suspension in the atmosphere.

the additional ground ice formed as a direct result of permafrost aggradation.

the cumulative number of degree-days below 0° C for the air temperature during a given time period.

an extensive body of the atmosphere in which physical properties, particularly temperature and humidity, exhibit only small and continuous differences in the horizontal plane; it may extend over an area of several million square kilometers and over a height of several kilometers.

the ambient temperature indicated by a thermometer exposed to the air but sheltered from direct solar radiation, or placed in an instrument shelter 1.5 to two meters above ground; also called surface temperature.

the cumulative number of degree-days above 0°C for the air temperature during a given period.

a large depression of the ground surface produced by thawing of a large area of very thick and exceedingly ice-rich permafrost.

a non-dimensional, unitless quantity that measures how well a surface reflects solar energy; ranges from 0 - 1; a value of 0 means the surface is a “perfect absorber,” where all incoming energy is absorbed, a value of 1 means the surface is a “perfect reflector,” where all incoming energy is reflected and none is absorbed.

a low centered on the eastern slope of the Canadian Rockies in the province of Alberta, Canada.

the low pressure center located near the Aleutian Islands on mean charts of sea level pressure during the winter; it represents one of the main centers of action in the atmospheric circulation of the northern hemisphere.

refers to high mountain areas above the timber line (where trees cease to inhabit extremely cold environments).

a glacier that is confined by surrounding mountain terrain; also called a mountain glacier.

annual accumulations of snow and dust on a glacier.

the lowest altitude at which mountain permafrost occurs in a given highland area outside the general permafrost region.

the vertical subdivision of an area of mountain permafrost into permafrost zones, based on the proportion of the ground that is perennially cryotic.

a principal middle level cloud type (cloud genus), white or gray, or both white and gray, which occurs as a layer or patch with a wave aspect, the elements of which appear as laminae, rounded masses, rolls, etc; these elements usually are sharply outlined, but they may become partly fibrous or diffuse; they may or may not be merged, and they generally have shadowed parts; most of the regularly arranged altocumulus elements have an apparent width of 1 - 5 degrees.

a principal middle level cloud type (cloud genus) in the form of a grayish (gray) or bluish cloud sheet or layer of striated, fibrous, or uniform appearance, totally or partly covering the sky; the layer has parts thin enough to reveal the position of the sun; halo phenomena do not usually occur.

any wind blowing up a steep incline or mountain; the opposite of katabatic wind.

in synoptic meteorology, a detailed study of the state of the atmosphere over a particular region based on the actual observations.

submerged ice which is attached to the bottom.

an instrument which measures wind speed or wind speed and direction; a cup anemometer measures the wind speed from the speed of rotation of a windmill which consist of 3 or 4 hemispherical or conical cups, each fixed to the ends of horizontal arms attached to a vertical axis; a byram anemometer is a variety of the cup anemometer; a counting anemometer has cups or a fan whose rotation is transmitted to a technical counter which integrates directly the air movement speed; a hand anemometer is small portable anemometer held at arm's length by an observer making a wind speed measurement; a pressure tube anemometer (dines anemometer) is an instrument which derives wind speed from measurements of the dynamic wind pressures - wind blowing into a tube develops a pressure greater than the static pressure, while wind blowing across a tube develops a pressure less than the static, this pressure difference is proportional to the square of the wind speed.

a Russian anemograph (recording anemometer) which is equipped with a device to record the wind direction in addition to wind speed.

a Russian anemometer combined with a vane to determine the wind direction.

an instrument for measuring atmospheric pressure; it is constructed on the following principles: an aneroid capsule (vidie capsule, which is a thin, disk-shaped box or capsule, usually metallic) is partially evacuated of gas, and is restrained from collapsing by an external or internal spring; the deflection of the spring will be nearly proportional to the difference between the internal and external pressures; magnification of the spring deflection is obtained both by connecting capsules in series and by mechanical linkages.

deviation of a meteorological quantity value in a given region from the normal (mean) value for the same period.

the line of latitude 66° 34′ S (often taken as 66.5° S); along this line the sun does not set on the day of the summer solstice, and does not rise on the day of the winter solstice.

also known as the antarctic convergence; the southern front of the antarctic circumpolar current that separates the antarctic zone in the south from the polar frontal zone in the north; taken by many to delineate the actual northern boundary of the antarctic zone; characterized by sea surface temperatures near 5°–6° C and a salinity minimum of 33.8–34.0 psu produced by high rainfall.

the region between the antarctic circle (66° 34′ S) and the South Pole; climatically, the limit of the zone may be set at about 60° S, poleward of which the prevailing westerly winds give place to easterly or variable winds; over most of this region the average temperature does not rise above 0°C (32°F) even in summer.

the prevention of ice accumulation of aircraft, ships and other objects; the most common measures are heating or applying a dressing by brush or spray to weaken adhesion and facilitate removal.

an ice wedge that grows progressively downwards into a receding slope, in a direction normal (perpendicular) to the surface.

area of increased atmospheric pressure relative to surrounding pressure field in the atmosphere; it is outlined by closed isobars on a synoptic surface chart, and by closed contours on a constant-pressure chart; this term is used interchangeably with high.

area of increased atmospheric pressure relative to surrounding pressure field in the atmosphere; outlined by closed isobars on a synoptic surface chart, and by closed contours on a constant-pressure chart; used interchangeably with high..

system of air movements (atmospheric circulation) associated with an anticyclone, which is clockwise in the northern hemisphere and counter-clockwise in the southern hemisphere.

the amount of heat required to raise the temperature of a unit mass of frozen ground by one degree.

the cumulative number of degree-days below 0 degrees Celsius for a given time period, calculated from the mean monthly temperatures for a specific station without making corrections for positive degree-days in spring and fall.

the cumulative number of degree-days above 0 degrees Celsius for a given time period, calculated from the mean monthly temperatures for a specific station without making corrections for negative degree-days in spring and fall.

(from Greek arktikos which means northern) northern polar region of the earth which includes almost the whole area of the Arctic Ocean and adjacent areas of Eurasian and North American continents.

mass of very cold air in the arctic regions which invades lower latitudes at irregular intervals.

the line of latitude 66 degrees 34 minutes N (often taken as 66.5 degrees N); along this line, the sun does not set on the day of the summer solstice, and does not rise on the day of the winter solstice.

(1) the semi-permanent, semi-continuous front between the deep, cold arctic air and the shallower, basically less cold polar air of northern latitudes (2) south boundary of the arctic air mass.

haze in arctic regions which reduces horizontal and slant visibility and which may extend to a height of about 10 km; it appears blue-grey when viewed away from the sun, and reddish-brown toward it.

a weak high which appears over the arctic basin during late spring, summer and early autumn; one of the centers of action in the atmosphere.

a mist of ice crystals; a very light ice fog.

an atmospheric circulation pattern in which the atmospheric pressure over the polar regions varies in opposition with that over middle latitudes (about 45 degrees N) on time scales ranging from weeks to decades; the oscillation extends through the depth of the troposphere, and from January to March, it extends upward into the stratosphere where it modulates in the strength of the westerly vortex that encircles the arctic polar cap region; the north atlantic oscillation and arctic oscillation are different ways of describing the same phenomenon.

evaporation (steam) fog produced above a surface of open water within arctic ice when the air is stable and relatively cold.

the northern limit of tree growth; the sinuous boundary between tundra and boreal forest; taken by many to delineate the actual southern boundary of the arctic zone.

(1) geographically, the area north of the arctic circle (66° 34′ N) (2) (same as tundra) biogeographically, the area extending northward from the arctic tree line; also used for the level above the timber line in mountains.

sharp, narrow ridge formed as a result of glacial erosion from both sides.

the process of inducing or maintaining a frozen condition in earth materials by artificial means.

the envelope of air surrounding the earth and bound to it more or less permanently by virtue of the earth's gravitational attraction; the system whose chemical properties, dynamic motions, and physical processes constitute the subject matter of meteorology.

the large-scale movement of air, and the means by which heat is distributed on the surface of the Earth; may vary from year to year.

as commonly used in weather observing practice, an observable occurrence of particular physical significance within the atmosphere; from the viewpoint of weather observations, the atmospheric phenomena include all hydrometeors (precipitation types and fogs), blowing snow, thunderstorms, tornadoes, waterspouts, and others.

pressure (force per unit area) exerted by the atmosphere on any surface by virtue of its weight; it is equivalent to the weight of a vertical column of air extending above a surface of unit area to the outer limit of the atmosphere.

longwave (infrared) radiation emitted by or being propagated through the atmosphere.

luminous phenomena, in the form of arcs, bands, draperies, or curtains in the high atmosphere over high latitudes; auroras are related to magnetic storms and the influx of charged particles from the sun, the phenomena are called aurora borealis in the northern hemisphere and aurora australis in the southern hemisphere.

mass of snow which becomes detached and slides down a slope, often acquiring great bulk by fresh addition as it descends.

arithmetic mean (m) of a number (n) of values (x1, x2, ... xn), defined by the equation: m = sxi/n; annual average value is calculated from 12 monthly means; daily average (or mean) value is calculated from 24 hourly readings of a meteorological element, or often from the average of the daily maximum and minimum values (for example, of temperature); monthly average is usually calculated as the average of the daily average values.

the semipermanent subtropical high over the North Atlantic Ocean, especially when it is located over the eastern part of the ocean; the same high over the western part of the Atlantic is called the Bermuda high; on mean charts of sea level pressure, this high is one of the primary centers of action in northern latitudes.

alternate bands of light and dark on a glacier; usually found below steep narrow icefalls and thought to be the result of different flow and ablation rates between summer and winter.

a distinct soil micromorphology, resulting from the effects of freezing and thawing processes, in which soil particles form subhorizontal layers.

a barometer that records barometric pressure over time (days or weeks).

an instrument for measuring atmospheric pressure; two types of barometers are commonly used in meteorology: the mercury barometer and the aneroid barometer.

areas of discontinuous vegetation cover in the polar semi-desert of the high arctic.

a layer of unfrozen ground that is perennially cryotic (t < 0 degrees Celsius), forming the basal portion of the permafrost.

the cryostructure of a frozen deposit of boulders that is saturated with ice.

the sliding of a glacier over bedrock.

the cryostructure of a frozen layered deposit of gravel and boulders that is saturated with ice.

a stream characterized by narrow reaches linking pools or small lakes.

an ocean and ice circulation pattern in the Beaufort Sea, north of Alaska. This gyre moves in a clockwise direction, fed by an average high-pressure system that fosters anti-cyclonic winds. Ice that forms in or drifts into the Beaufort Gyre has historically remained in the Arctic ice system for years, accumulating snow and thickening each winter. Beginning in the late 1990s, the ice began melting away while in the southern parts of the gyre, before completing the circulation.

hard-packed rock lying below the Earth’s surface; lies in beds or layers; can be variable across geographic space; above bedrock is a layer of broken, weathered rock.

a long area of pack ice from a few km to more than 100 kilometers in width.

crevasse that separates flowing ice from stagnant ice at the head of a glacier.

large chunk of glacier ice (a very small iceberg) floating in the sea; bergy bits are usually less than 5 meters (15 feet) in size and are generally spawned from disintegrating icebergs.

the semipermanent subtropical high over the North Atlantic Ocean, especially when it is located over the western part of the ocean; the same high over the eastern part of the Atlantic is called the Azores high; on mean charts of sea level pressure, this high is one of the primary centers of action in northern latitudes.

situation of a vessel surrounded by ice and unable to move.

an extensive crescent-shaped indentation in the ice edge, formed either by wind or current.

a lead closed off on all sides within the ice pack.

winds of at least 35 miles per hour along with considerable falling and/or blowing snow reducing visibility to less than one-quarter mile for a period of at least three hours (extremely cold temperatures are often associated with dangerous blizzard conditions, but are not a formal part of the modern definition).

a surficial layer of angular shattered rocks formed in either modern or pleistocene periglacial environments.

opening through a snow bridge into a crevasse or system of crevasses which are otherwise sealed by snow bridges; a snowdrift usuallly forms on the lee side.

an ensemble of snow particles raised by the wind to moderate or great heights above the ground; the horizontal visibility at eye level is generally very poor.

a cold wind blowing down an incline; a kind of katabatic wind.

the forested region that adjoins the tundra along the arctic tree line, which has two main divisions: its northern portion is a belt of taiga or boreal woodland, while its southern portion is a belt of true forest, mainly conifers but with some hardwoods; on its southern boundary the boreal forest passes into “mixed forest” or “parkland,” prairie, or steppe, depending on the rainfall.

icebergs that originate from near the bottom of a glacier; the color is usually black from trapped rock material or dark blue because of old, coarse, bubble-free ice; they sit low in the water due to the weight of the embedded rocks.

temperature measured at the base of the snow cover during mid- to late-winter (February/March).

glacier that has one or more tributary glaciers that flow into it; distinguished from a simple valley glacier that has only a single tributary glacier.

accumulation of floating ice made up of fragments not more than 2 meters (6.6 feet) across, the wreckage of other forms of ice.

small droplets of highly saline water that form in pockets between ice crystals, as sea ice forms and expels salt into the underlying ocean water.

method to predict the presence or absence of permafrost in a mountain area, using measurements of the bottom temperature of snow cover mid- to late-winter.

smooth hills of ice that form on the bottom of sea ice from eroding keels, particularly during the summer melt.

a buoy, either fixed or floating, which carries instruments for sensing various meteorological elements and for transmitting the data by radio.

ice formed or deposited on the ground surface and later covered by sediments.

break off from a larger ice shelf or ice sheet into the water.

process by which ice breaks off a glacier's terminus; usually the term is reserved for tidewater glaciers or glaciers that end in lakes, but it can refer to ice that falls from hanging glaciers.

glacier that loses material by calving, usually a glacier that terminates in sea, lake, or river water.

a semipermanent mass of firn formed by drifted snow behind obstructions or in the ground; also called a snowdrift glacier or a drift glacier.

ice formed in a closed or open cave.

striations or marks left on the surface of exposed bedrock caused by the advance and retreat of glacier ice.

a warm wind blowing down an incline; a kind of katabatic wind.

the large-scale cyclonic circulation in the middle and upper troposphere centered generally in the polar region; also called polar vortex.

bowl shape or amphitheater usually sculpted out of the mountain terrain by a cirque glacier.

glacier that resides in basins or amphitheaters near ridge crests; most cirque glaciers have a characteristic circular shape, with their width as wide or wider than their length.

a principal high-level cloud type (cloud genus), appearing as a thin, white patch or layer of cloud without shading, composed of very small elements in the form of grains, ripples, etc., merged or separated, and more or less regularly arranged; most of the elements have an apparent width of less than 1 degree.

a principal high-level cloud type (cloud genus), appearing as a transparent, whitish cloud veil of fibrous (hair-like) or smooth appearance, totally or partially covering the sky, and often producing halo phenomena, either partial or complete.

a principal high-level cloud type (cloud genus), appearing as detached clouds in the form of white, delicate filaments or white or mostly white patches or narrow bands; these clouds have a fibrous (hair-like) appearance, or a silky sheen, or both; because cirrus elements are too narrow, they do not produce a complete circular halo.

sky with a total cloud cover of less than one okta (or one-tenth in the united states).

synthesis of weather conditions in a given area, characterized by long-term statistics (mean values, variances, probabilities of extreme values, etc.) of the meteorological elements in that area; polar climate (arctic climate) is generally the climate of a geographical polar region, most commonly taken to be a climate which is too cold to support the growth of trees.

a study dealing with variations in climate on many different time scales from decades to millions of years, and the possible causes of such variations; (1) in the most general sense, the term climate change encompasses all forms of climatic inconstancy (that is, any differences between long-term statistics of the meteorological elements calculated for different periods but relating to the same area) regardless of their statistical nature or physical causes; climate change may result from such factors as changes in solar activity, long-period changes in the earth's orbital elements (eccentricity, obliquity of the ecliptic, precession of equinoxes), natural internal processes of the climate system, or anthropogenic forcing (for example, increasing atmospheric concentrations of carbon dioxide and other greenhouse gases) (2) the term climate change is often used in a more restricted sense, to denote a significant change (such as a change having important economic, environmental and social effects) in the mean values of a meteorological element (in particular temperature or amount of precipitation) in the course of a certain period of time, where the means are taken over periods of the order of a decade or longer.

representation of the climate system based on the mathematical equations governing the behavior of the various components of the system and including treatment of key physical processes and interactions, cast in a form suitable for numerical approximation with computers.

(1) in the most general sense, the term climate variability denotes the inherent characteristic of climate which manifests itself in changes with time; the degree of climate variability can be described by the differences between long-term statistics of meteorological elements calculated for different periods, (in this sense, the measure of climate variability is the same as the measure of climate change) (2) the term climate variability is often used to denote deviations of climate statistics over a given period of time (such as a specific month, season or year) from the long-term climate statistics relating to the corresponding calendar period; (in this sense, climate variability is measured by those deviations, which are usually termed anomalies).

atlas composed mainly of climatological charts; it represents especially the monthly and annual distributions of the principal climatic elements of a specific region for a relatively long period.

the scientific study of climate; the aspect of meteorology which studies processes of climate formation, distribution of climates over the globe, analysis of the causes of differences of climate (physical climatology), and the application of climatic data to the solution of specific design or operational problems (applied climatology); climatology may be further subdivided according to purpose or point of view: agricultural climatology, air-mass climatology, aviation climatology, bioclimatology, dynamic climatology, medical climatology, macroclimatology, mesoclimatology, microclimatology, paleoclimatology, synoptic climatology, etc..

ice formed in a closed space, cavity or cave in permafrost.

composed of close ice that is mostly in contact; ice cover 7/10ths to 9/10ths.

a layer or body of unfrozen ground occupying a depression in the permafrost table below a lake or river.

freezing that occurs under conditions that preclude the gain or loss of any water by the system.

a pingo formed by doming of frozen ground due to freezing of injected water supplied by expulsion of pore water during permafrost aggradation in the closed talik under a former water body.

a hydrometeor consisting of a visible aggregate of minute particles of liquid water or ice, or both, suspended in the free air and usually not touching the earth's surface; it may also include larger particles of liquid water or ice (precipitation particles) and non-aqueous liquid or solid particles such as those present in fumes, smoke and dust (aerosols); cloudiness is the same as cloud cover; but usually it is used in a very general sense.

that portion of the sky cover which is attributed to clouds; the unit of measurement is the okta or tenths (meaning one-eighth or one-tenth) of the sky dome as seen by the observer.

decrease in volume per unit volume of a substance resulting from a unit increase in pressure, under isothermic conditions.

any non-occluded front that moves in such a way so that colder air replaces warmer air; the leading edge of a relatively cold air mass.

glacier in which most of the ice is below the pressure melting point; nonetheless, the glacier's surface may be susceptible to melt due to incoming solar radiation, and the ice at the rock/ice interface may be warmed as a result of the natural (geothermal) heat from the earth's surface.

at a given level in the atmosphere, any low that is generally characterized by colder air near its center than around its periphery; the opposite of a warm low.

the location that has the lowest annual mean temperature in its hemisphere.

that portion of a peatland where the whole or part of a palsa or peat plateau has thawed and collapsed to the level of the surrounding peatland.

a wedge showing evidence of both primary and secondary filling.

flow that occurs when glacier motion is decelerating down-slope.

the physical process by which a vapor becomes a liquid or solid; the opposite of evaporation; in meteorological usage, this term is applied only to transformation from vapor to liquid; any process in which a solid forms directly from its vapor is termed sublimation, as is the reverse process.

the transport of energy entirely resulting from the random motions of individual molecules, and not from any concerted group movement; occurs in response to temperature gradients; contrasts with convection, in which energy is transported by molecules moving together in coherent groups.

an advanced form of new ice that forms as a stable sheet with a smooth bottom surface.

a distinct soil micromorphology, resulting from the effects of freezing and thawing processes, in which coarser soil particles form compound arrangements.

pack ice in which the floes are frozen together; ice cover 10/10ths.

special design and construction procedures required when engineering works are undertaken in permafrost areas.

snow metamorphism that adds molecules to sharpen the comers and edges of an ice crystal.

geographic area in which permafrost occurs everywhere beneath the exposed land surface with the exception of widely scattered sites, such as newly deposited unconsolidated sediments that have just been exposed to the freezing climate; mean annual soil surface temperatures are typically below -5 degrees Celsius (23 degrees Fahrenheit).

the major subdivision of a permafrost region in which permafrost occurs everywhere beneath the exposed land surface with the exception of widely scattered sites.

the transport of energy resulting from the concerted movement of molecules in coherent groups; contrasts with conduction in which energy is transported by the random motions of molecules; atmospheric convection is nearly always turbulent and results in the vertical transport and mixing of atmospheric properties.

cumuliform cloud which forms in the atmosphere as a result of convection; such clouds are also called clouds of vertical development, a cloud that has its base in the low height range but extends upward into the middle or high altitudes.

apparent force, due to the rotation of the earth, which acts normal to, and to the right of the velocity of a moving particle in the northern hemisphere, the movement of the particle being considered relative to that of the earth.

an overhanging accumulation of ice and wind-blown snow, characteristically found on the edge of a ridge or cliff face.

any fracture or rift in floating ice not sufficiently wide to be described as a lead.

a way that snow or ice can move by deforming its internal structure.

the slow deformation (or time-dependent shear strain) that results from long-term application of a stress too small to produce failure in the frozen material.

the failure strength of a material at a given strain rate or after a given period under deviatoric stress.

open fissure in the glacier surface.

a kind of hoarfrost; ice crystals that develop by sublimation in glacial crevasses and in other cavities with cooled space and calm, still conditions under which water vapor can accumulate; physical origin is similar to depth hoar.

a hard snow surface lying upon a softer layer; crust may be formed by sun, rain or wind, and is described as breakable crust or unbreakable crust, depending upon wh