Anomalous onset date of the first rainy season in South China and its relationship with the variation of the atmospheric circulation and SST

Using the NCEP/NCAR reanalysis data, the NOAA Sea Surface Temperature (SST) data, the CMAP precipitation data and the rainfall observations from the 261 stations in South China from 1961 to 2012, the anomalous climatic characteristic of the onset date of the first rainy season (OSFRS) in South China was analyzed. The relationship between OSFRS in South China with the variations of the atmospheric circulation and preceding SST on March-April were analyzed by the correlation and composite analysis methods. The results showed that OSFRS in South China had significant interannual variation in the last 52 years, but its the variation trend wasn't obvious. the earliest OSFRS in South China was on March 1, 1983, the latest was on June 1, 1963. The mean OSFRS during 1961-2012 was on April 6. OSFRS in South China were usually in March and April (account for 92.3%). There was a significant correlation between OSFRS in South China and the precipitation in March-April in South China, with the precipitation in March-April in South China more (less) in years of earlier (later) OSFRS in South China. In March-April of the years of earlier OSFRS in South China, the subtropical westerly jet stream was stronger compared with the mean in the upper troposphere, the western North Pacific subtropical high was stronger and shifts westwards in mid-troposphere, the southwest air current was stronger in South China and the south branch trough was stronger in the lower troposphere, but was opposite in the years of later OSFRS in South China. There was significant correlation between OSFRS in South China and SST in March-April in the South China Sea and its surrounding areas. The SST of the South China Sea and its surrounding areas was lower (higher) while in the years of later (earlier) OSFRS in South China. The atmospheric circulation and SST anomaly in the years of later OSFRS in South China was more notable than that in earlier year.