Time-lagged effects of spring Tibetan Plateau soil moisture on the monsoon over China in early summer

The objective of the present study is to investigate the effect of initial soil moisture in the Tibetan Plateau (ISMTP) during the spring period on the local and regional climate in subsequent months. Numerical experiments with different ISMTP are made from 1 April to 30 June for the year 1998 using a regional climate model. This was a wet year with anomalously high summer precipitation over China. The same experiments have also been done for the year 1995, which was a normal year with respect to the summer rainfall over China. In both years, the snow amount over the Tibetan Plateau (TP) was higher than normal in the preceding winter/spring. The results of the experiments indicated that an increase in the ISMTP may lead to decreases in the air temperature, vertical velocity, and surface heating over the TP in June. In addition to the local effects, an increase in the ISMTP may also lead to modifications of the climate in some remote regions in early summer, such as an increase in the amount of monsoon precipitation over the mid to lower reaches of the Yangtze River region in eastern China and a decrease over the south China region. These precipitation differences due to the changes in ISMTP are consistent with those due to anomalous snow cover over the TP in winter or spring. Physically, the Tibetan High is weakened with an increase in ISMTP, which leads to a change in the strength of the Asian summer monsoon. Copyright (C) 2007 Royal Meteorological Society.