A one-dimensional model of a freezing and thawing ground with a seasonally varying surface cover was analyzed. Analytical and numerical techniques were used primarily to study the factors that produce differences between the yearly means of the air and ground temperatures. It was shown that the variation of the surface cover characteristics in phase with the annual air temperature wave can generate the heat-valve effect which is responsible for raising the average ground temperature above the average air temperature. This temperature difference was, however, very sensitive to changes to the surface cover properties indicating how disturbances to the surface cover could cause melting of a permafrost soil.

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