Impacts of land surface and sea surface temperatures on the onset date of the South China Sea summer monsoon

The present study analyzes the differences in spatial and temporal variations of surface temperatures between early and late onset years of the South China Sea summer monsoon (SCSSM). It is found that when the land surface temperature north of 40A degrees N is lower (higher) and the sea surface temperature over the South China Sea-western North Pacific (SCS-WNP) is higher (lower) in winter, the onset of the SCSSM begins earlier (later). When the land surface temperature north of 40A degrees N is higher (lower) and the sea surface temperature over the SCS-WNP is lower (higher) in spring, the onset of the SCSSM occurs earlier (later). The reason why the anomalies of the land surface temperatures north of 40A degrees N can influence the atmospheric circulation is investigated by analysis of the wind and temperature fields. In order to verify the mechanisms of influence over the land and sea surface temperature distribution patterns and test the ability of the p-sigma regional climate model (p-sigma RCM9) to simulate the SCSSM onset, three types of years with early, normal, and late SCSSM onset are selected and the SCSSM regimes are numerically simulated. According to the results obtained from five sensitive experiments, when the land surface temperature is higher in the eastern part, north of 40A degrees N, and lower in the western part, north of 40A degrees N, and it rises faster in the eastern coastal regions and the Indian Peninsula, while the sea surface temperatures over the SCS-WNP are lower, the early onset of the SCSSM can be expected.