Comparison of the effects of soil moisture and El Niño on summer precipitation in eastern China

Abstract

The effects of spring soil moisture over the vast region from the lower and middle reaches of the Yangtze River valley to North China (YRNC) and El Nino on the East Asian summer monsoon (EASM) and precipitation in eastern China, as well as the relevant mechanisms, are investigated using the modified atmospheric model ECHAM5 coupled with the Common Land Model. These models are the atmospheric and land components of the climate system model developed at the Chinese Academy of Meteorological Sciences (CAMS-CSM). The simulations show that both soil moisture anomalies in eastern China and El Nino sea surface temperature (SST) anomalies have significant influences on the EASM, with the effect of soil moisture being slightly greater than that of the El Nino. However, the impacts of soil moisture on EASM and rainfall in eastern China are markedly different from those of the El Nino. Wetter (drier) soil over the YRNC corresponds to less (more) precipitation over northern and southeastern China, and more (less) precipitation over the Yangtze River basin and northeastern China, as well as a strengthened (weakened) and westward-shifted (eastward-shifted) West Pacific Subtropical High and a deepened (shallower) East Asian trough, representing a weakened (strengthened) EASM pattern. During El Nino developing summers, an anomalous anticyclone extends from northeastern to northern China, and an anomalous cyclone occupies the middle and lower reaches of the Yangtze River and southern China. Concurrently, the West Pacific Subtropical High is anomalously weaker than normal. As a result, rainfall anomalously increases over the lower reaches of the Yangtze River and southern China, and decreases over northern and northeastern China. In El Nino decaying summers, there is an anomalous cyclone over northeastern China and an anomalous anticyclone over southern China. The convergence of southerly airflow and northerly winds leads to enhanced rainfall around northern China and the middle reaches of the Yangtze River, and reduced rainfall over other regions.