The Relationship Between June Precipitation over Mid-Lower Reaches of the Yangtze River Basin and Spring Soil Moisture over the East Asian Monsoon Region

Using the US Climate Prediction Center (CPC) soil moisture dataset and the observed precipitation over China together with the NCEP/NCAR reanalysis wind and air temperature, the relationship between June precipitation over mid-lower reaches of the Yangtze River basin (MLR-YRB) and spring soil moisture over the East Asian monsoon region was explored, with the signal of the ENSO effect on precipitation removed. A significant positive correlation was found between the mean June precipitation and the preceding soil moisture over the MRL-YRB. The possible response mechanism for this relationship was also investigated. It is found that when the soil over the MRL-YRB is wetter (drier) than normal in April and May, the air temperature in the lower troposphere over this region in May is lower (higher) than normal, and this temperature effect leads to a decrease (increase) in the temperature contrast between the land and the sea. Generally, a decrease (increase) in the land-sea temperature contrast leads to weaker (stronger) East Asian summer monsoon in June. Southerly (northerly) wind anomalies at 850 hPa then show up in the south of the Yangtze River basin while northerly (southerly) wind anomalies dominate in the north. These anomalies lead to the convergence (divergence) of wind and water vapor and hence gives rise to more (less) precipitation in June over the MLRYRB.