Interannual Variation of the Early Spring Extreme Cold Days over the Tibetan Plateau and the Possible Mechanisms

It is widely known that the Tibetan Plateau (TP) has great impacts on the regional and global weather/climate by the dynamic and thermodynamic forcing. As the key region, the climate of the TP is receiving more and more attention. Low temperature is one of the typical meteorological disasters, exerting serious effects on the livestock farming over the TP. Therefore, in the present study, the possible mechanisms of the interannual variability of the early spring extreme cold days (ECD) over the TP are probed into, and our analyses suggest that the factors contributing to the TP ECD in March and April are markedly diverse. In March, the local anomalies of the snow cover and cyclone over the TP provide a suitable background for the occurrence of the ECD by changing the surface heat flux and leading to the adiabatic cooling and increase of the cloud cover related to the ascending motion, respectively. Further study indicates that the synergetic effect of the Arctic Oscillation and Western Pacific pattern is conducive to the formation of the aforementioned cyclonic anomaly over the TP. However, in April, the local cold temperature advection along with the significant northerly/northwesterly anomalies over the TP favors the condition for the more ECD on the interannual timescale. The Eurasian pattern and tripolar pattern of the anomalous North Atlantic sea surface temperature are found to show the crucial impacts on the concurrent TP ECD through stimulating the wave trains individually and producing the above local horizontal winds anomalies over the TP.