Two distinct patterns of spring Eurasian snow cover anomaly and their impacts on the East Asian summer monsoon

The Eurasian snow cover anomaly in spring has been considered as one of the important factors affecting East Asian summer monsoon (EASM). The spring snow cover data for the period from 1972 to 2004 are used to extract dominant spatial patterns over the Eurasian region and to examine their impacts on the EASM through empirical orthogonal function (EOF) analysis. The first EOF mode is generally characterized by a continent-wide snow cover anomaly over the whole Eurasian region, while the second EOF mode is dominated by an east-west dipole structure over Eurasia. Our study indicates that the variability of dipole pattern snow cover is more closely related to the EASM rainfall than that of continent-wide snow cover. A strong dipole pattern with positive (negative) snow cover anomalies over western Eurasia and negative (positive) snow cover anomalies over eastern Eurasia signifies enhanced (reduced) summer rainfall over East Asia, and the Eurasian wave train pattern is apparent. An important implication of these results is that the spring snow cover anomaly over Eurasia provides a complementary precursor for EASM variability.