Different mechanisms of Eurasian snow cover on precipitation during the early and late pre-rainy season in South China

The interannual variability in precipitation during the pre-rainy season (PRS) in South China is significantly correlated with Eurasian snow cover. This study elucidates the distinct mechanisms by which Eurasian snow cover anomalies in March influence 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 midlatitude 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, and the related upper-level divergence, ascending motion, and moisture convergence in South China are intensified, collectively promoting precipitation there. In contrast, during the late PRS, increased snow cover across the eastern sector of Eastern Europe (EEE) and the region east of Lake Baikal (ELB) inhibit South China’s precipitation. The wave pattern associated with the EEE (ELB) snow anomaly propagates southeastwards (southwards) 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 resulted in 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 the two periods, lending credence to the proposed mechanisms.