Regional integrated environmental model system and its simulation of East Asia summer monsoon

A continuous 22-year simulation in Asia for the period of 1 January 1979 to 31 December 2000 was conducted using the Regional Integrated Environmental Model System (RIEMS 2.0) with NCEP Reanalysis II data as the driving fields. The model processes include surface physics state package (BATS 1e), a Grell cumulus parameterization, and a modified radiation package (CCM3) with the focus on the ability of the model to simulate the summer monsoon over East Asia. The analysis results show that (1) RIEMS reproduces well the spatial pattern and the seasonal cycle of surface temperature. When regionally averaged, the summer mean temperature biases are within 1–2°C. (2) For precipitation, the model reproduces well the spatial pattern, and temporal evolution of the East Asia summer monsoon rain belt, with steady phases separated by more rapid transitions, is reproduced. The rain belt simulated by RIEMS 2.0 is closer to observation than by RIEMS 1.0. (3) RIEMS 2.0 can reasonably reproduce the large-scale circulation.