Thermal regimes at the snow–ground interface and their implications for permafrost investigation

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Snow cover is a critical factor determining the presence or absence of permafrost in mid-latitude high mountain regions. This paper discusses the relation between temporal changes in temperature at the snow–ground interface and permafrost distribution. Four fundamental types of temporal change in winter ground surface temperature (GST) are identified: (1) nearly constant at 0 °C, (2) short-term fluctuation, (3) gradual increase without short-term fluctuation, and (4) gradual decrease without short-term fluctuation. The latter three are favorable for permafrost growth, and result from direct cold penetration throughout winter, ground cooling before the onset of seasonal snow cover and cold air funneling and concentrating in voids between coarse blocks, respectively. The fourth thermal effect predominantly contributes to growth of permafrost, and thus should be included in the bottom temperature of snow cover (BTS) concept which involves mainly the third effect. Monitoring GST over a winter provides a new tool for investigating the distribution of permafrost, as well as information on the thermal regimes that control permafrost development.