1) Arctic geography terminology 
In environments containing permafrost, the active layer is the top layer of soil that thaws during the summer and freezes again during the autumn. In all climates, whether they contain permafrost or not, the temperature in the lower levels of the soil will remain more stable than that at the surface, where the influence of the ambient temperature ...
(from the article `permafrost`) ...upper surface of permafrost is called the permafrost table. In permafrost areas the surface layer of ground that freezes in the winter (seasonally ... ...snowmelt and summer rains is available for plant growth. In addition, most tundra and polar barrens are underlain by soils that are permanently ... ...
Upper zone of soil in higher latitude locations that experiences daily and seasonal freeze-thaw cycles.
The seasonally thawed zone above permafrost.
(in arctic or subarctic regions) the layer of soil, above the permafrost, that thaws during the summer.