Interannual Variation in the Mid-Summer Rainfall over the Western Sichuan Basin and the Associated Circulation Anomalies

Interannual variation of the mid-summer（July and August） rainfall over the western Sichuan Basin and associated lower-tropospheric circulation anomalies are analyzed by using the rainfall data at 730 stations provided by the Chinese Meteorological Data Center, and the National Centers for Environmental Prediction/National Center for Atmospheric Research（NCEP/NCAR） reanalysis data. The lower-tropospheric circulation anomalies associated with greater and lesser amounts of rainfall over the western Sichuan Basin are examined. More rainfall over the western Sichuan Basin corresponds to a significant southerly anomaly over the basin, suggesting a stronger occurrence of the Southwest Vortex and a northward displaced subtropical high over the western Pacific. Less rainfall over this basin corresponds to more significant circulation anomalies but with opposite signs, suggesting a weaker Southwest Vortex and a southward shift of the subtropical high. Moreover, interannual variation in mid-summer rainfall in the western Sichuan Basin has a positive and significant correlation with that in Northwest China and North China and a negative and significant correlation with that in South China. These correlations can be explained by the lower tropospheric circulation anomalies.