frozen ground or permafrost

seasonally-active permafrost

the uppermost layer of the permafrost which undergoes seasonal phase changes due to the lowered thawing temperature and freezing-point depression of its pore water.

seasonally thawed layer (STL)

the active layer in permafrost areas.

seasonally thawed ground

ground that thaws and refreezes annually.

seasonally frozen layer (SFL)

the active layer in areas without permafrost.

seasonally frozen ground

ground that freezes and thaws annually.

seasonal thawing index

the cumulative number of degree-days above 0 degrees Celsius, calculated as the arithmetic sum of all the positive and negative mean daily air temperatures (degrees Celsius) for a specific station during the time period between the lowest point in the spring and the highest point the next fall on the cumulative degree-day time curve.

seasonal frost

the occurrence of ground temperatures below 0 degrees Celsius for only part of the year; see also active layer.

seasonal freezing index

the cumulative number of degree-days below 0 degrees Celsius, calculated as the arithmetic sum of all the negative and positive mean daily air temperatures (degrees Celsius) for a specific station during the time period between the highest point in the fall and the lowest point the next spring on the cumulative degree-day time curve.

sand-wedge polygon

a polygon outlined by sand wedges underlying its boundaries.

sand wedge

a wedge-shaped body of sand produced by filling of a thermal contraction crack with sand either blown in from above or washed down the walls of the crack.

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