青藏和伊朗高原热力异常与北疆夏季降水的关系

青藏高原和伊朗高原热力异常对其周边地区天气气候有重要影响,已有研究多关注东部季风区,而对干旱区关注较少.针对这一不足,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北疆43站降水资料,分析了1961-2007年5月青藏高原和伊朗高原地表感热异常与北疆夏季降水的关系.奇异值分解(SVD)分析发现,5月青藏高原地表感热与北疆夏季降水呈负相关,伊朗高原为正相关.青藏高原和伊朗高原感热异常的大尺度对比,要比仅考虑单一高原的感热异常与北疆夏季降水有更密切的联系.定义了一个热力差异指数来表征这种地表感热异常的对比程度,相关分析发现,当5月伊朗高原地表感热偏强,青藏高原地表感热偏弱时,500hPa中亚上空和贝加尔湖上空分别为异常气旋和反气旋环流,在二者共同作用下,新疆上空盛行异常的偏南气流,有利于低纬度的暖湿气流北上,形成有利于降水的环流形势,同时越赤道索马里急流偏强,低纬度水汽被接力输送至中亚和新疆地区,为降水的发生提供了有利的水汽条件.进一步分析发现,青藏高原热力异常主要影响中高层大气环流,伊朗高原则主要影响水汽通量输送.

Relationships between the anomalies of surface sensible heat in the Tibetan Plateau and Iran Plateau and summertime precipitation in North Xinjiang

The surface thermal anomalies(STA)in the large orography have important influences on the climate.Previous studies were focused on the effects of the S'hA in the'hibetan Plateau on the weather and climate in China with less attention paid to the connection between the STA in the Iran Plateau and the precipitation in the arid regions,especially in Xinjiang.In this paper, we give preliminary results of the relationship between the STA in the'hibetan Plateau and Iran Plateau and summer rainfall in North Xinjiang.By use of the NC EP/NC AR rcanalysis monthly mean data and the precipitation data at the 43 stations in North Xinjiang, the relationships between the anomalies of surface sensible heat in the Tibetan Plateau and Iran Plateau and the summcrtime precipitation in North Xinjiang were analyzed.Icy Singular Value Decomposition CSVIO method,they were found that the sen a negative correlation with sible heat in the Tibetan Plateau has summcrtime precipitation in North Xinjiang,and it in the Iran Plateau has a positive correlation with summertime precipitation.The anomaly contrast of surface sensible heat between the Tibetan Plateau and the Iran Plateau has a closer relation than that in any single region with summertime precipitation in North Xinjiang.Therefore,an index is defined to reflect the intensity of the large-scale thermal contrast between the two plateaus.By correlation analysis,it were found that when the strong sensible heat in the Iran Plateau and weak sensible heat in the Tibetan Plateau in May occurred,there were an anomalous cyclone over C entral Asia and an anomalous anticyclone over the Baikal Lakc at 500 hPa respectively, which resulted in the anomalous south wind prevailing and was favorable to the warm-wet air moving from the low latitude regions.In addition,the transportation of water vapor by the Somalia jet stream was unusually strong, passing over the Equator, and at the same time the Arabian Sca is controlled by anomalous anticyclone circulation,driving the water vapor to be transferred continuously to the Central Asia and Xinjiang.Above all were contributed to the occurrence of more summer precipitation in North Xinjiang, and vice versa.Further analysis found that the thermal anomalies in the Tibetan Plateau have closer relations with the mid-upper troposphere circulations,but the thermal anomalies in the Iran Plateau have closer relations with the water vapor flux.