Impacts of Tibetan Plateau Winter and Spring Snow Depth Anomalies on Summer Precipitation in Yunnan and Possible Mechanism

Based on the snow depth dataset over China and CN05-gridded precipitation data over China, the relationship between the snow depth in the Tibetan Plateau (TP) and summer precipitation in Yunnan is investigated through singular vector decomposition and correlation analysis. Results show that the positive snow depth anomalies in the central and western TP during winter and spring can enhance the summer precipitation in Yunnan, particularly in the Jinsha River basin and the southwest of Yunnan, and the correlations between the snow depth in the TP and the summer precipitation in Yunnan may be independent of the influence of the El Niño–Southern Oscillation. The possible impact mechanism has been investigated through diagnostic analyses using the fifth generation ECMWF reanalysis datasets (ERA5). The extreme snow depth in the key region of the TP leads to a low surface air temperature in the central and western parts of the TP and nearby areas in spring. This is conducive to the late onset of the South Asian summer monsoon and leads to a weak South Asian summer monsoon and the associated monsoon depression, along with the abnormal westerly wind to the south of the TP. Moreover, the cold surface temperature associated with the extreme snow depth in the TP can initiate the wave train at 200 hPa, which propagates from the western part of the TP through Mongolia to Northeast Asia along the westerly jet stream. Furthermore, an anomalous cyclonic circulation can be observed in Northeast Asia, which is conducive to the southward movement of cold air in the middle and high latitudes, leading to increased rainfall in Yunnan. Meanwhile, a wave train at 850 hPa, which spreads from the southwest side of the plateau to the South China Sea, can be observed, leading to an anomalous anticyclonic circulation in the South China Sea. An anomalous low-level shear over Yunnan develops due to the westerly wind on the southern side of the plateau and the southwesterly wind on the northwest side of the anticyclonic circulation in the South China Sea, which is favorable for increased precipitation in Yunnan. Meanwhile, cold air flows southward to Yunnan and converges with warm and humid air, which also contributes to the increased summer precipitation in Yunnan.