| Section P | P index | 151-159 of 747 terms |
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permafrost table—(Also called pergelisol table.) The more or less irregular surface in the ground that marks the upper limit of the permafrost; not to be confused with frost table.
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permafrost—1. (Also called perennially frozen ground, pergelisol, permanently frozen ground.) A layer of soil or bedrock at a variable depth beneath the surface of the earth in which the temperature has been below freezing continuously from a few to several thousands of years. Permafrost exists where the summer heating fails to descend to the base of the layer of frozen ground. A continuous stratum of permafrost is found where the annual mean temperature is below about −5°C (23°F).Compare pereletok; see active layer. 2. As limited in application by P. F. Svetsov, soil that is known to have been frozen for at least a century.
Muller, S. W., 1947: Permafrost, or Permanently Frozen Ground, and Related Engineering Problems,
Hare, F. K., 1951: Compendium of Meteorology, p. 958, and map, p. 956.
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permanent anticyclone—A high that exists in approximately the same location most of the year, every year, and thus is evident on long-term average annual mean charts.
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permanent control—A stable cross section of a channel, often man-made or on bedrock, that is used for monitoring measurements of depth and velocity.
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permanent depression—A low that exists in approximately the same location most of the year, every year, and thus is evident on long-term average annual mean charts.
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permanent echo—(Abbreviated PE.) A radar echo from a stationary object, such as a building, a hill, or power lines, that may interfere with the detection or measurement of other kinds of echoes. See ground clutter.
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permanent gas—A gaseous component of the atmosphere with its mixing ratio nearly constant with time and height.
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