Cryosphere glossary
tropopause
the boundary layer between the troposphere and stratosphere, where an abrupt change in temperature lapse rate usually occurs; it is defined as the lowest level at which the lapse rate decreases to 2 degrees Celsius per kilometer or less, provided that the average lapse rate between this level and all higher levels within 2 kilometers does not exceed 2 degrees Celsius per kilometer; occasionally, a second tropopause may be found if the lapse rate above the first tropopause exceeds 3 degrees Celsius per kilometer.
troposphere
lower part of the atmosphere, extending from the surface up to a height varying from about 7 to 9 kilometers (4.3 to 5.6 miles) at polar regions to approximately 17 kilometers (10.6 miles) in tropics; characterized by decreasing temperature with height, appreciable vertical wind motion, appreciable water vapor content, and weather.
trough
in meteorology, an elongated area of relatively low atmospheric pressure; the opposite of a ridge.
tundra
treeless terrain, with a continuous cover of vegetation, found at both high latitudes and high altitudes.
turbic cryosol
a mineral soil showing marked evidence of cryoturbation, as indicated by broken horizons and displaced material.
turf hummock
a hummock consisting of vegetation and organic matter with or without a core of mineral soil or stones.
turf-banked (solifluction) lobe
a solifluction lobe with its front covered by a vegetation mat.
turf-banked (solifluction) terrace
a solifluction terrace with its front covered by a vegetation mat.
two-layer permafrost
ground in which two layers of permafrost are separated by a layer of unfrozen ground.
two-phase thermosyphon
a passive heat transfer device, filled with a temperature-dependent liquid/vapour combination, installed to remove heat from the ground.
ultraviolet radiation
electromagnetic radiation of shorter wavelength than visible radiation but longer than x-rays; roughly, radiation in the wavelength interval from 10 to 4000 angstroms.
unbreakable crust
a hard snow surface lying upon a softer layer; may be formed by sun, rain or wind, and is described as breakable crust or unbreakable crust, depending upon wether it will break under the weight of a turning skier.
unfrozen ground
soil or rock that does not contain any ice.
unfrozen water content
the amount of unfrozen (liquid) water contained in frozen soil or rock.
uniaxial compression test
a method to determine the short-term strength of rocks; conducted by employing a constant loading rate until failure; the failure load is used to calculate the failure stress; can also be used to determine the elastic constants of rocks (i.e. Young's modulus, Poisson's ratio).
unstable air
air in which static instability prevails; this condition is determined by the vertical gradients of air temperature and humidity.
upper air observation
an observation made in the free atmosphere either directly or indirectly.
upper atmosphere
the general term applied to the atmosphere above the mesopause.
upward freezing
the advance of a freezing front upwards from the permafrost table during annual freezing of the active layer.
valley glacier
a mountain glacier whose flow is confined by valley walls.