Effects of Thermal Contrast between Central Asia and South Asia on Summer Rainfall over the Tarim Basin

In the present study, the NCEP/NCAR reanalysis monthly mean data and the rainfall data collected at 83 stations in Xinjiang are used to analyze the possible influences of the thermal contrast between Central Asia and South Asia on summer rainfall over the Tarim Basin. The results show that the summer rainfall over the Tarim Basin is closely related to temperature in the middle and lower troposphere over Central Asia and South Asia. When positive and negative temperature anomalies occur in middle and lower troposphere over South Asia and Central Asia respectively, an anomalous cyclone over Central Asia and an anomalous anticyclone over the Mongolia at 500 hPa will develop, resulting in southerly wind anomalies that prevail over the Tarim Basin, which is favorable for the transport of warm, moist air from the low latitude regions. At the same time, the anomalous anticyclones over the Arabian Sea and central Asia lead to the two-step transport of water vapor from the Arabian Sea to Central Asia and the Tarim Basin. The temperature in the middle and lower troposphere over central Asia mainly affects the atmospheric circulation at 500 hPa especially over Central Asia, and the temperature in the middle and lower troposphere over South Asia plays a more important role in water vapor transport. Further analysis indicates that the enhanced summer monsoon over the Tibetan Plateau corresponds to anomalous anticyclone at 600 hPa over the northern side of the Tibetan Plateau; this anomalous anticyclone is favorable for the southward movement of cold air from high latitudes, which leads to the middle and lower tropospheric cooling over central Asia. The significant sea surface temperature (SST) warming has a close relation with temperature change in the middle and lower troposphere over South Asia.