Evaluation of Meiyu prediction in the Yangtze-Huaihe region by coupled Ocean-Atmosphere General Circulation Model (BCC_CM1.0)

Based on the output data of Coupled OceanAtmosphere General Circulation Model (BCC-CM1.0) of National Climate Center, the meiyu in the YangtzeHuaihe regio n ensemble prediction experiment is performed to verify the prediction ability o f the BCC-CM1.0 from 1978-2006. The results show that BCC-CM1.0 can predict the basic meiyu spatial pattern and the leading EOF mode. The predicted rain bel t is obviously north than the observation, so it causes more precipitation to th e north of the Yangtze River and predicts less precipitation to the south of the Yangtze River. Additionally, it shows that the medium intensity meiyu rainfall has been forecasted better than the high and low intensity rainfall. Synthetic a nalysis shows that BCC -CM1.0 can forecast the difference of meiyu rainfall bet ween meiyu forecasting good years and meiyu forecasting poor years, it has good performance when rain belt locates north and meiyu rainfall less; otherwise the model performs poorly. Geopotential height field forecasted by BCC-CM1.0 is substantially weaker t han the observation, especially in the QinghaiTibet Plateau and Western Pacifi c Subtropical High region, which causes barometric gradient over East Asian mons oon areas increasing and East Asian monsoon enhancing, therefore, enhanced East Asian monsoon maybe one reason that results in moving northward of rain belt in YangtzeHuaihe area in BCC-CM1.0. Furthermore, poor forecasting of moisture c ontent may also contribute to moving northward of rain belt in the YangtzeHuai he region.