第二届未来大气科学论坛

The interannual variability of precipitation during the pre-rainy season (PRS) in South China exhibits a significant correlation with the Eurasian snow cover. This study elucidates the distinct mechanisms of Eurasian snow cover anomalies in March on precipitation during the early (pre-monsoon) and late (post-monsoon) PRS. In the early PRS, anomalous snow cover in the western region of Eastern Europe (WEE) triggers a southeastward-propagating wave train that impacts Central Asia. The teleconnection pattern induces anomalous cyclonic circulation in Central Asia, which reinforces the mid-latitude zonal wind, contributing to the zonal wind wave train pattern towards East Asia. As a result, the East Asian subtropical westerly jet and the western North Pacific subtropical high are enhanced. Consequently, the related upper-level divergence, ascending motion, and moisture convergence in South China are intensified, collectively promoting precipitation there. Contrarily, during the late PRS, increased snow cover across the eastern sector of Eastern Europe (EEE) and the region east of Lake Baikal (ELB) exerts an inhibitory effect on South China’s precipitation. The wave patterns associated with the EEE (ELB) snow anomaly propagates southeastward (southward) to lower latitudes, intensifying the western North Pacific subtropical high. Furthermore, the perturbation stemming from the ELB region induces negative geopotential height anomalies aloft and amplifies the baroclinic anticyclone over the western Pacific. This results in a prevailing subsidence over South China, which in turn suppresses precipitation during the late PRS. Numerical experiments corroborate the observed circulation adjustments and precipitation responses to snow cover anomalies in two periods, lending credence to the proposed mechanisms.

Eurasian snow cover; pre-rainy season; South China; wave train