Interannual Variability of Winter Precipitation over the Western Side of Tibetan Plateau and Its Impact Factors

Based on monthly precipitation datasets of the Global Precipitation Climatology Centre (GPCC) and the Global Precipitation Climatology Project (GPCP) and daily ERA-Interim reanalysis data, characteristics of winter precipitation over the western side of Tibetan Plateau (TP) from 1979 to 2012 and the impact factors of interannual precipitation variability in this region are investigated in the present study. Results indicate that winter precipitation over the TP mainly occurs over the western side and the principal spatial pattern is uniform. The moisture source for precipitation is largely from upstream areas and enters the TP from the western boundary. However, the interannual variability of winter precipitation over the western side of TP is mainly explained by the dynamic component of the moisture transport, which is featured by a southwesterly circulation anomaly over the western side of TP. Besides, the interannual variability of winter precipitation over the western side of TP is more related to SST (sea surface temperature) in the equatorial oceans than to the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO) over upstream regions. The anomalous SST over the central and eastern tropical Pacific Ocean can affect the atmospheric circulation, triggering anticyclonic anomaly over the northern Indian Ocean and southwesterly anomaly over the west side of TP, which further enhance the dynamic process of moisture transport. Besides, under the influence of the tropical easterly anomalies, warm ocean water is transported to the western Indian Ocean and accumulates there. The anomaly of the equatorial SST also regulates the meridional location of the westerly jet, which further affects wintertime moisture transport and interannual variability of precipitation over the western side of TP.