Objective Quantification of Moisture Transport that Influences Summer Rainfall in the Middle and Lower Reaches of the Yangtze River

Daily wind, specific humidity, and surface pressure data from NCEP/NCAR, and monthly average rainfall data from 160 stations of National Climate Center in China are used to examine summer rainfall-influencing moisture transport in the middle and lower reaches of the Yangtze River. Results show the moisture originates along the south boundary. On the basis of this, area, center intensity, eastern ridge point, and boundary intensity indices are defined. It can be found that the moisture transport influences rainfall in different areas over China in summer through correlation analysis. A significant turning point comes in the 1990s to all indices. There're obvious interdecadal changes in indices of area, central intensity, and zonal intensity in the boundary. Correlation analysis shows that moisture transport influences summer rainfall in different areas over China, and that area and center intensity indices are negatively correlated with the western Pacific SST, but positively correlated with the eastern and equatorial Pacific SST. It also shows that higher winter eastern Pacific SST strengthens moisture transport from the western Pacific during summer, which enhances summer rainfall in the middle and lower reaches of the Yangtze River .