Meridional Variation of South Asian High and Its Relationship with the Summer Precipitation over China

South Asian High (SAH) is the most intense and stable upper level anticyclone in boreal summer. As a member of the East Asian Summer Monsoon system, SAH plays an important role in the regional climate anomaly over China.The meridional variation of SAH is analyzed by using the monthly mean data derived from the European Center for Medium-Range Weather Forecasts (ECMWF) 40-year reanalysis (ERA-40) from 1958 to 2002. An index of SAH (SAHI) is defined to measure its meridional variation in summer and to analyze its relationship with the summer precipitation over China. The results show a significant correlation between the meridional position of SAH and the summer rainfall over China for both the interannual timescale variability and the long-term linear tendency. The correlation coefficients between SAHI and the summer rainfall in North China and in the Yangtze River Valleys are 0.577 and-0.604, respectively, both of which exceeds 0.01 level. When SAH locates further northward (southward), North China and South China are wetter (drier) than normal, while the Yangtze River Valleys is drier (wetter) than normal. And the southward linear trend of SAH corresponds with the decreasing trend of rainfall in North China and the increasing trend of rainfall in the Yangtze River Valleys.Linear regression analysis of the circulation reveals that when SAH locates further northward, an anomalous anticyclone controls eastern China with its center tilted southward from 200 hPa to 850 hPa. In the upper atmosphere, the anomalous anticyclone forms a divergence zone over North China. In the lower atmosphere, it results in flows diverging over the Yangtze River valley, and converging over North China. Besides, the northward movement of SAH would cause the upper-level westerly jet and the Western Pacific Subtropical High move northward, with the rainbelt locating in North China.The meridional anomalous variation of SAH is closely related to the sea surface temperature anomalies (SSTA) of the Tropical Indian Ocean (TIO), the Central and Eastern Equatorial Pacific, and the northern Pacific. And the TIO SSTA might modulate its meridional position directly. Positive TIO SSTA might lead to a southward expansion of SAH.Due to strong correlation with the summer rainfall over China and being modulated by the TIO SSTA, the meridional variation of SAHI could be considered as an important indicator used to predict the regional climate anomaly.