Water Vapor Transport around the Tibetan Plateau and Its Effect on Summer Rainfall over the Yangtze River Valley

The water vapor transport around the Tibetan Plateau (TP) and its effect on the rainfall in the Yangtze River valley (YRV) in summer are investigated by decomposing the moisture transport into rotational and divergent components. Based on the ERA-Interim and PREC/L (Precipitation Reconstruction over Land) data from 1985 to 2014, the vertically integrated features of the two components are examined. The results show that the divergent part dominates the western TP while the rotational part dominates the rest of the TP, implying that moisture may be mostly locally gathered in the western TP but could be advected to/from elsewhere over the rest of the TP. The divergent and rotational moisture fluxes exhibit great temporal variability along the southern periphery of the TP, showing sensitivity of water vapor to the steep topography there. Correlation analysis reveals that it is over the southeastern corner of the TP and to its south that a significant correlation between rotational zonal moisture transport and summer rainfall in the YRV appears, suggesting that the southeastern corner of the TP may serve as a moisture transport bridge between the South Asian (Indian) monsoon and the East Asian monsoon. Further composite analysis indicates that anomalous eastward (westward) zonal water vapor transport from the South Asian monsoon via the southeastern corner of the TP favors more (less) precipitation in the YRV in summer.