Snow and Ground Temperature

A numerical model of snow-ground thermal interactions has been developed to investigate the effect of seasonal snow cover on the mean annual ground temperature. The model is parameterized in terms of three snow event parameters: onset time of the annual snow event, duration of the event, and maximum depth of snow during the event. These parameters are commonly available from meteorological and remotely sensed data making the model broadly applicable. The model is validated using surface air temperature (SAT), surface ground temperature (SGT), and snow depth data from observations at Emigrant Pass climate observatory (EPO) in northwestern Utah and National Weather Service data from sites across North America. Measured subsurface temperature-time series compare well with changes predicted by the model. We define a "snow effect" as the difference in mean annual ground temperatures with and without a snow event and explore how the snow effect might change with a warming climate. During the period 1950-2002, the mean North American snow event onset (December 15) and duration (81 days) has remained relatively constant although interannual variation as much as 18 days (onset) and 15 days (duration) are present. Across all North American stations with snow cover during this period, the trend in mean annual SGT-SAT offset is about \- 0.02 K/decade. One unanticipated finding is that snow can either raise or lower the mean annual ground temperature depending principally on the timing of the snow event.