Preliminary Research on Moisture Transport Anomalies in Two Interdecadal Changes in Summer Precipitation in South China

Based on the reanalysis data provided by the National Centers for Environmental Prediction/National Center for Atmospheric Research and the daily rainfall data obtained at 2374 stations by the China Meteorological Administration, the precipitation moisture transport was found to have increased during the 1993–2002 period and decreased during the 2003–2012 period over South China. In this study, the characteristics of this precipitation transport were compared using a moisture transport budget equation, and the reason for the two decadal changes in the summer precipitation in South China was determined. Our results show that the increase (decrease) in summer precipitation during the 1993–2002 (2003–2013) period in South China was mainly influenced by the local circulation of the vertical air stream, eastward (westward) movement of the South Asia high, and the westward (eastward) extension of the West Pacific subtropical high (WPSH), which resulted in a strengthening (weakening) of the moisture transport from the Philippines and the southwest side of the WPSH and a strong convergence (divergence) of moisture in the lower layer over South China. The interdecadal variation of the summer precipitation of South China is mainly related to anomalies in the dynamic divergence of the moisture transport caused by changes in wind speed. It is also affected by an anomaly of the thermodynamic divergence of the moisture transport caused by a change in the specific humidity and an anomaly in the subseasonal-scale eddies generated by synoptic-scale eddies. In addition, we found the moisture transport anomalies to be closely related to the circulation and sea-surface-temperature anomalies.