Cryosphere glossary
active liquid refrigerant pile
a foundation pile on which a liquid coolant refrigeration system has been installed to remove heat from the ground.
active rock glacier
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.
active thermokarst
the process by which characteristic landforms are currently developing as a result of thawing of ice-rich permafrost or melting of massive ice.
active-layer failure
a general term referring to several forms of slope failures or failure mechanisms commonly occurring in the active layer overlying permafrost.
active-layer thickness
the thickness of the layer of the ground that is subject to annual thawing and freeing in areas underlain by permafrost.
adfreeze strength
the tensile or shear strength which has to be overcome to separate two objects that are bonded together by ice.
adfreeze/adfreezing
the process by which two objects are bonded together by ice formed between them.
advance
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.
advection
the horizontal transfer of air mass properties by the velocity field of the atmosphere.
advection fog
fog which forms in the lower part of a warm moist air mass moving over a colder surface (land or water).
aerosol
non-gaseous substances, divided into solid particles or liquid droplets, held in suspension in the atmosphere.
aggradational ice
the additional ground ice formed as a direct result of permafrost aggradation.
air freezing index
the cumulative number of degree-days below 0° C for the air temperature during a given time period.
air mass
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.
air temperature
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.
air thawing index
the cumulative number of degree-days above 0°C for the air temperature during a given period.
alas/alass
a large depression of the ground surface produced by thawing of a large area of very thick and exceedingly ice-rich permafrost.
albedo
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. This quantity can also be expressed as a percent with a range from 0 to 100, with zero percent absorbing all incoming energy and 100 percent reflecting all energy.
Alberta low
a low centered on the eastern slope of the Canadian Rockies in the province of Alberta, Canada.
Aleution low
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.