https://cdn.earthdata.nasa.gov/conduit/upload/5182/KeywordsCommunityGuide_Baseline_v1_SIGNED_FINAL.pdf 23.7 2026-04-15T10:53:30.610Z https://gcmd.earthdata.nasa.gov/KeywordViewer/scheme/sciencekeywords/c82f3480-545f-4491-83f1-0477369ddcd8 PERMAFROST Date=2015-12-10 User Id=aaleman Entity=NarrowerRelation Operation=INSERT User Note=Insert Concept System Note=add narrower relation New Value=PERMAFROST [c82f3480-545f-4491-83f1-0477369ddcd8,84051] - PERMAFROST TEMPERATURE [d8606e80-3d34-4540-a355-5f99737f7ab7,158553] 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 5C (23F). <p>2. As limited in application by P. F. Svetsov, soil that is known to have been frozen for at least a century. <p> Muller, S. W., 1947: Permafrost, or Permanently Frozen Ground, and Related Engineering Problems, <p> Hare, F. K., 1951: Compendium of Meteorology, p. 958, and map, p. 956. 2015-12-10 17:11:34.0