Circulation Differences in Anomalous Rainfall over the Yangtze River and Huaihe River Valleys in Summer

Both the Yangtze River and the Huaihe River lie in mid-latitudes in East Asia, and so the large-scale circulation and climatic background of weather events in the Yangtze River valley and the Huaihe River valley are similar. However, there are different interannual variations between anomalous rainfall events in the Yangtze River valley and in the Huaihe River valley in summer. This study focuses on differences in circulation in middle to high latitudes in Asia and middle to low latitudes in the southern hemisphere, and the associated mechanisms. Both physical and statistical methods were used in this study. We looked at the differences in Asian circulation for anomalous rainfall events in the Yangtze River basin and the Huaihe River valley in summer. East Asian subtropical westerly winds at 200 hPa strengthened (weakened) and a longitudinal (zonal) pattern with anomalous geopotential height at 500 hPa occurred in middle to high latitudes over East Asia. Meanwhile, the locations of both the Australian anticyclone and the Mascarene anticyclone shifted further east (west), respectively, than normal, the cross-equatorial flow strengthened in the areas 150°E to 180° and weakened in the areas 50°E to 60°E (weakened in the areas 150°E to 180° and strengthened in the areas 50°E to 60°E), and anomalous rainfall in summer occurred in the Yangtze River valley (the Huaihe River valley). Thus, the intensity of East Asian subtropical westerly winds as well as the locations of both the Australian anticyclone and the Mascarene anticyclone played an important role in the occurrence of anomalous rainfall events in the Yangtze River valley and the Huaihe River valley in summer.