Impact of East Asian Winter Monsoon on Rainfall over Southeastern China and its Dynamical Process

The present study investigates the impact of the East Asian winter monsoon (EAWM) on winter (January-February-March, or JFM in short) rainfall over southeastern China (including South China and central eastern China) and its dynamical process by using station observations for the period 1951-2003 and the ERA-40 reanalysis for the period 1958-2002. It is found that there is a significant correlation between interannual variations of the EAWM and JFM rainfall over southeastern China. Analyses show that in weak EAWM years southwesterly anomalies at 700 hPa dominate over South China Sea, which transports more moisture into South China, favoring rainfall increase. At the same time, the East Asian westerly jet weakens and displaces southward, contributing to the increase of ascending motion over Southeastern China. The air temperature over southeastern China shows an obvious decrease at 300 hPa and increase near the surface. This enhances the convective instability and weakens the potential vorticity (PV), which explains the strengthening of ascending motion and the increase of JFM rainfall over southeastern China. In addition, the JFM rainfall anomalies over central eastern China is closely related to the EAWM, and rainfall anomalies over South China is closely related to both ENSO and the EAWM.