Relationship between the boreal spring Hadley circulation and the summer precipitation in the Yangtze River valley

The connection between the boreal spring Hadley circulation (HC) and variability of the following summer east Asian atmospheric circulations and precipitation in the Yangtze River valley is investigated through an analysis of the observed data in this study. It is found that there is a significantly positive correlation between HC and the summer rainfall in the Yangtze River valley. This relationship is well supported by the changes of atmospheric general circulation backgrounds and water vapor conditions related to the variation of the preceding boreal spring HC. The summer situations of strengthened western Pacific subtropical high (WPSH), intensified South Asian high (SAH), southward located east Asian jet (EAJ) and enhanced water vapor corresponding to strong spring HC provide favorable conditions for increasing the precipitation in the Yangtze River valley and vice versa. The possible mechanism how the boreal spring HC affects summer atmospheric circulations is identified preliminarily in the study. Results show that sea surface temperature (SST) anomalies in the Indian Ocean and South China Sea may play an important role in linking the spring HC and summer atmospheric circulations. Spring HC may evoke SST anomalies in the Indian Ocean and South China Sea, which can persist from spring to summer and in turn give rise to anomalous east Asian summer monsoon. As a result, summer rainfall in the Yangtze River valley may be influenced.