Snow influences atmospheric circulation through its effects on diabatic heating and the hydrologic cycle which are determined by the extent, depth and location of the snow-covered surface. Thus a study of continental-scale seasonal and interannual variability of both observed snow cover and snow depth is a necessary step for understanding the natural variability of the snow and its impact on the climate system. Several studies have focused on seasonal and interannual variability of snow cover; however, so far there has been no similarly detailed study of snow depth. This study addresses this need and both seasonal snow cover and snow depth variability are examined.
General circulation models simulate snow water equivalent which may be related directly to snow depth and not snow cover. The observed snow depth variability established here is thus a useful baseline is assessing the ability of a general circulation model to simulate seasonal snow water equivalent and also in determining whether snow anomalies prescribed in past snow sensitivity studies have been realistic.
The seasonal climatology and standard deviation of Northern Hemisphere snow cover and snow depth is established using global data sets based on satellite sensors. The annual cycle of snow cover and depth and the interannual variability of seasonal snow cover, snow depth and snow extent from the two data sets are examined for various regions. A decrease in spring snow extent for both North America and Eurasia has been found by previous studies using the snow cover data; in this study, the geographic distribution of the linear trend in snow cover frequency is studied by analyzing the linear trend in three month sliding seasons progressing from winter to the following autumn. It is shown that there has been a decrease in snow cover frequency of up to 10% per decade for certain regions in the midlatitudes during the spring seasons.
Complete copies of this report are available from:
Center for Ocean-Land-Atmosphere Studies
last update: 22 December 1997
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