1. (North-American usage) Permafrost underlying 35 to 65 percent of the area of exposed land surface; 2. (Russian usage) Permafrost underlying 40 to 60 percent of the area of exposed land surface
(1) (North American usage) permafrost underlying 35 - 65% of the area of exposed land surface (2) (Russian usage) permafrost underlying 40 - 60% of the area of exposed land surface.
As a general term, any water mass found at intermediate depth in the ocean. Antarctic Intermediate Water is the most important of these, followed by Subarctic Intermediate Water and Arctic Intermediat
e Water. Other water masses identified as intermediate water are Atlantic Intermediate Water in Baffin Bay, also called Polar Atlantic Water, identified by a temperature maximum at a depth of about 500 m resulting from inflow from the West Greenland Current; Arctic Intermediate Water in Baffin Bay, identified by a temperature minimum at a depth between 50 and 200 m resulting from inflow of arctic water from the north; and Levantine Intermediate Water in the Eurafrican Mediterranean Sea, identified by a salinity maximum at a depth between 150 and 400 m and formed when cold winter winds, descending on the region between Rhodes and Cyprus and on the northern and central Adriatic Sea, result in the cooling and sinking of surface water.
Loss of mass from a glacier by melting of ice or firn between the summer surface and the bed. See mass-balance units. Internal ablation can occur due to strain heating of temperate ice as the ice defo
rms. However, the largest heat sources for internal ablation are likely to be the potential energy released by downward motion of the ice and of meltwater. The magnitude of the former is equivalent to a few mm w. E. A-1, and of the latter, which occurs mainly in conduits transferring water from the glacier surface to the bed, to up to a few tens of mm w. E. A-1. (These rates are expressed over the extent of a typical valley glacier.)
Refreezing of water within a glacier, between the summer surface and the bed, which goes undetected by measurements of surface mass balance. See mass-balance units, zone. Accumulation beneath the summ
er surface is the refreezing of surface meltwater (or freezing of rain) that is in transit and otherwise would have left the glacier as runoff. In the case of meltwater, it may be regarded as redistributing mass within the glacier. This may require careful accounting in the calculation of mass balance. Internal accumulation proceeds by the freezing of water that percolates early in the ablation season into firn that is still cold, heating the firn in the process, or by the freezing of retained pore water during the accumulation season, also releasing latent heat and thus slowing the downward advance of the winter cold wave. The term is reserved for refreezing beneath the summer surface, that is, within the firn or the ice. Meltwater that refreezes within the snow does not constitute internal accumulation since it is accounted for by end-of-season density measurements as part of conventional mass-balance measurements. Internal accumulation may be small in magnitude, and negligible on temperate glaciers, but if not accounted for it constitutes a bias towards overestimation of mass loss. In remote-sensing studies, it is not always possible to detect the summer surface. In addition models of the surface mass balance do not always distinguish between internal accumulation and refreezing within the snow. To avoid confusion, it is advisable to use 'internal accumulation' only in the sense given above and to use the more inclusive 'refreezing' only for 'internal accumulation plus refreezing within the snow'. Refreezing within the snow should be described as such explicitly.
A layer within the atmosphere bounded below by the surface, and above by a more or less sharp discontinuity in some atmospheric property. Internal boundary layers are associated with the horizontal ad
vection of air across a discontinuity in some property of the surface (e.g., aerodynamic roughness length or surface heat flux) and can be viewed as layers in which the atmosphere is adjusting to new surface properties. See thermal internal boundary layer, mechanical internal boundary layer.
A measure of the compactness, or strength of the ice; plays an important role in the deformation of the ice and formation of features such as ridges and leads.