Cryosphere glossary
design thawing index
the cumulative number of degree-days above 0 degrees Celsius, calculated by taking the average of the seasonal thawing indices for the three warmest summers in the most recent 30 years of record.
destructive metamorphism
snow metamorphism that rounds the comers and edges of an ice crystal.
detachment failure
a slope failure in which the thawed or thawing portion of the active layer detaches from the underlying frozen material.
dew point
the temperature to which a given parcel of air must be cooled at constant pressure and constant water-vapor content in order for saturation to occur; when this temperature is below 0 degrees Celsius, it is called the frost point.
diamond dust
a type of precipitation composed of slowly falling, very small, unbranched crystals of ice which often seem to float in the air; it may fall from a high cloud or from a cloudless sky, it usually occurs under frosty weather conditions (under very low air temperatures).
dielectric constant
measure of the ability of the soil to store electrical energy in the presence of an electrostatic field.
dilation crack
a tensile fracture in a frozen material due to surface extension caused by doming.
dilation crack ice
ice that forms in dilation cracks.
dip pole
either of the two points on the earth's surface at which magnetic meridians converge; the horizontal component of the magnetic field of the earth becomes zero at this point; also called the magnetic pole.
dipole anomaly
An Arctic atmospheric pressure pattern characterized by high pressure centered over the northern Beaufort Sea and unusually low pressure centered over the Kara Sea. This pattern contributes to ice loss in summer, causing winds to blow ice away from the coast.
dirt cone
a cone-shaped formation of ice that is covered by dirt; a dirt cone is caused by a differential pattern of ablation between the dirt covered surface and bare ice.
dirty ice
ice that contains sediments stirred up and tangled in the ice as it grows.
Image
Terry Whitledge, National Oceanic and Atmospheric Administration/Department of Commerce
discontinuous permafrost
permafrost occurring in some areas beneath the exposed land surface throughout a geographic region where other areas are free of permafrost.
discontinuous permafrost zone
the major subdivision of a permafrost region in which permafrost occurs in some areas beneath the exposed land surface, whereas other areas are free of permafrost.
disequilibrium permafrost
permafrost that is not in thermal equilibrium with the existing mean annual surface or sea-bottom temperature and the geothermal heat flux.
draft
the thickness of sea ice extending below the water level. Draft and freeboard comprise total sea ice thickness.
drain channel
preferred path for meltwater to flow from the surface through a snow cover.
drift glacier
a semipermanent mass of firn formed by drifted snow behind obstructions or in the ground; also called a catchment glacier or a snowdrift glacier.
drift ice
ice that moves from winds, currents, or other forces.
drift of ice
displacement of a sea ice field from its place of origin under the effect of ocean currents and winds.