Multi-year simulation of the East Asian Monsoon and Precipitation in China using a Regional Climate Model and Evaluation

By using the regional climate model (RegCM??NCC), East Asian monsoon and precipitation over China during 1998 to 2002 are simulated. Results show that the model can well reproduce the seasonal patterns of mean circulation as well as the intensity and seasonal march of the East Asian monsoon. The simulated onset or retreat time of the West Pacific subtropical high, and the intensity and location of the South Asian high are consistent with the fact. The spatial distribution and transport of moisture in lower layer are also well simulated. The seasonal variations of regional rainfall and temperature are reproduced in the model, with three northward shift time and intensity of the rain belts over the sub-regions (such as Mid-Lower Yangtze basins and South China) well corresponding to the observation. However, the simulated summer monsoon is stronger compared with NCEP reanalysis fields, with the location of subtropical high being further north by 2-3 degrees than normal. Error evaluation shows that there is a discernible systematic bias in the simulated mean circulation pattern, with air temperature bias being positive over the land and negative over the ocean in the lower troposphere in summer. The systematic bias exaggerates the summer temperature difference between the land and ocean, which may be a main responsible factor for the stronger simulated summer monsoon, thus resulting in the overestimated rainfall in North China and it can not reflect well the abnormal rainfall distribution in these 5 years. The de ciency may be mainly contributed to the complex topography and cloud-radiation parameterization scheme. The analyses also indicate that it is difficult to simulate the persistent abnormal precipitation pattern over China. It is necessary to improve the model's capability further.