Variability of regional snow cover in spring over western Canada and its relationship to temperature and circulation anomalies

摘要

This study documents the variability of spring snow cover over the western Canadian Prairies and Northern Boreal Forest and its relationship to sea surface temperature (SST) over the North Pacific and atmospheric circulation over the North Pacific-North America. The work is based on monthly snow cover extent (SCE) estimates derived from Advanced Very High Resolution Radiometer data during 1972-2008. Results show that the SCE along eastern parts of the Canadian Rocky Mountains has the largest variance during March and April. Two regional SCE indices are defined using area mean SCE anomalies over the region of 47-53°N, 104-111°W (SCE-A) and 55-60°N, 111-120°W (SCE-B) based on the leading empirical orthogonal function (EOF) patterns of SCE in March and April, respectively. These two SCE indices are not only significantly correlated with simultaneous and preceding winter 500 hPa heights over mid-latitude northwestern North America and central North Pacific but also with SST in mid-latitude eastern North Pacific in preceding autumn and winter. Furthermore, it is found that the SST anomalies in the mid-latitudes along the western coast of North America in the preceding autumn-winter influence the 500 hPa height over northwestern North America in April and cause the variations of SCE-B. Finally, it is shown that the SCE-B can be used as a climatic index to characterize the connection of SCE with the regional skin temperature in late spring and early summer.