Role of May surface temperature over eastern China in East Asian summer monsoon circulation and precipitation

Abstract

Spring soil moisture over the vast region from the lower and middle reaches of the Yangtze River valley to North China (YRNC) can significantly influence East Asian summer monsoon (EASM) via May surface temperature. This study further validates the role of May surface temperature in linking spring soil moisture with summer monsoon circulation and rainfall over eastern China. The role of May surface temperature over YRNC in the ensuing EASM and precipitation over eastern China are investigated by observational analyses and numerical simulations. Given the long “memory” of soil temperature (ST) and its highly consistent with surface temperature, experiments are performed by altering ST as a substitution. The results show that YRNC spring surface temperature anomalies have a significant influence on EASM and precipitation over eastern China. The negative May ST anomalies correspond to an abnormal cooling in the surface and tropospheric atmosphere around the YRNC, which narrows the land-ocean thermal contrast, resulting in a weakened EASM. An anomalous anticyclone extends from southeastern China to the Philippine Islands, and an anomalous cyclone occupies northeastern China. Consequently, rainfall anomalously decreases over southeastern China and increases over northeastern China. The convergence of warm and humid southerly airflows and cold northerly winds conduces to an enhanced rainfall around the Yangtze River valley. The opposite occurs for the positive ST anomalies. Further simulations show that abnormal wet (dry) spring soil can lead to negative (positive) ST and surface temperature anomalies in May over the YRNC. Hence, the surface air temperature in May is the bridge for the effect of the YRNC spring soil moisture on the EASM and precipitation over eastern China.