Using updated actual observations of snow cover, soil moisture, and atmospheric circulation, we find that strong Indian summer monsoon precipitation is preceded by warmer than normal temperatures (and reduced snow cover) over Europe and North America in the previous winter and over western Asia in the previous spring, but only for the periods 1870-1895 and 1950-1995. This relationship has now disappeared. The European temperature anomalies are related to the positive phase of the North Atlantic Oscillation. After snow melts in the spring in Asia, soil moisture has a memory of one month at most in the upper 10 cm layer, and less than two months in the upper 1 m layer. Therefore, soil moisture cannot prolong a snow cover anomaly signal long enough to influence surface temperatures and the monsoon and there is no obvious relationship between soil moisture and the monsoon. By examining the same relationships in climate models, both in long control runs and in anthropogenically-forced transient runs, we conclude that the snow cover/monsoon relationship occurs by chance. The recent strong relationship is not a manifestation of global warming. Snow cover is a not a robust predictor of the monsoon.
Supplementary URL: