The Bridging Role of Eurasian Winter Snow in the Relationship between East Asian Winter and Summer Monsoons

A bridging role of the winter snow anomaly over northern China and southern Mongolia is found in the relationship between the East Asian winter monsoon (EAWM) and the East Asian summer monsoon (EASM) in both observations and model experiments. Results show that northern China and southern Mongolia (NCSM) region is a key location, in which both the EAWM and the EASM are sensitive to its winter snow anomaly.

Enhanced snow over NCSM and vicinity results in local surface and tropospheric cooling, strengthening the EAWM through cold air intrusion induced by northerly wind anomaly. In turn, the stronger EAWM provides a favorable condition for the formation of EA snowfall, indicating an interactive snow-EAWM positive feedback. The continental cooling persists from winter to early summer due to the snowmelt and moistening in spring, associated with a northward shift of the upper-level westerlies in early summer. Correspondingly, anomalous upward motion appears over northeastern China and downward motion occurs over the subtropical EA-Pacific region, resulting in a dipole rainfall pattern in EA with reduced rainfall over the Yangtze River basin (the core EASM regions) and increased rainfall over northeastern China. However, there exist evident differences in rainfall and circulation patterns between observation and model simulation, which need further investigation in near future. It is also found that the winter snow may exert a greater impact on early-summer monsoon compared to the late-summer monsoon.