Relation between Eurasian snow cover, snow depth, and the Indian summer monsoon: An observational study

Satellite-derived snow cover data for 22 yr and snow depth data for 9 yr ov er Eurasia have been analyzed to reexamine the possible relation of snow wi th the Indian summer monsoon. In contrast to the previous studies that use snow cover averaged over all of Eurasia as a single number, the frequency o f occurrence of snow at each grid point over Eurasia is correlated with the Indian summer monsoon rainfall. Thus specific geographical regions over Eu rasia that are responsible for the well-known inverse relationship between Eurasian snow cover and Indian monsoon rainfall are delineated. It is found, somewhat surprisingly, that western Eurasia is the only geogra phical region for which a significant inverse correlation exists between wi nter snow cover and subsequent summer monsoon rainfall. However, composites for high and low snow cover over Eurasia show spatially homogeneous large- scale patterns of snow cover and surface temperature anomalies. Winters of high and low snow cover for Eurasia are found to be associated with colder and warmer than normal temperatures, respectively, for large regions of the Eurasian continent. The inverse snow-monsoon relationship holds especially in those years when snow is anomalously high or low for both the winter as well as the consecutive spring season. Contrary to previous findings, no s ignificant relation is found between the Himalayan seasonal snow cover and subsequent monsoon rainfall.