中亚和南亚热力差异对塔里木盆地夏季降水的影响

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

利用美国国家环境预测中心/美国国家大气研究中心(NCEP/NCAR)再分析月平均资料和新疆83站降水资料,分析了1961~2010年南亚和中亚对流层中低层热力差异对塔里木盆地夏季降水的可能影响机制。研究结果表明,塔里木盆地夏季降水与中亚和南亚对流层中低层温度密切相关。当南亚对流层中低层偏暖,中亚偏冷时,500 h Pa中亚上空和蒙古上空分别为异常气旋和反气旋环流,在二者共同作用下,塔里木盆地上空盛行异常的偏南气流,有利于低纬海洋的暖湿气流北上,形成有利于降水的环流条件。同时阿拉伯海上空为异常反气旋环流,中亚上空为异常气旋环流,形成塔里木盆地夏季降水水汽的两步型输送,阿拉伯海水汽被输送至中亚和新疆地区。中亚对流层中低层温度变化主要影响500 h Pa环流,南亚对流层中低层温度变化在低纬水汽向北输送过程中扮演主要角色。青藏高原夏季风偏强时,600 h Pa高原北侧对应异常反气旋环流,异常偏北风引导高纬度冷空气南下,导致中亚区域对流层中低层偏冷,而南亚对流层中低层偏暖则与热带印度洋显著增暖密切相关。

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 h Pa 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 h Pa 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 h Pa 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.