Modulations of rising motion and moisture on summer precipitation over the middle and lower reaches of the Yangtze river

The contributions of vertical motion and moisture to the variation in summer precipitation over the middle and lower reaches of the Yangtze River over the period from 1960 to 2012 summers are documented in this study. Based on partial regression analysis, it is noted that both local vertical motion and moisture are significantly related to changes in summer precipitation. The temporal variation of the precipitation is well reproduced by considering both vertical motion and moisture. Furthermore, we separated the changes in summer precipitation into a linear trend and variation (detrended value). It is noted that the linear trend is contributed solely by the trend in vertical motion. Subsequently, we examined the trend in vertical motion with a continuity equation. The result signifies that the trend in vertical motion is caused by a decreasing trend in static stability in the lower troposphere. On the other hand, the variation is controlled by both vertical motion and moisture. The change in vertical motion is forced by the anomalous convergence in the midtroposphere and static stability in the lower troposphere. The change in moisture is contributed by the anomalous convergence of moisture transport. These changes are related to the southwestward extension of the western North Pacific subtropical high.