Downscaling Interpretation of NCC_CGCM Products for the Summer Precipitation over the Mid lower Reaches of the Yangtze

With February initial fields, NCC_CGCM model is run and the products (height field at 500 hPa, zonal wind and meridional wind fields at 200 hPa and 850 hPa) are compared with NCEP observation during 1983—2002 to study their relations. Although the differences between the observations and NCC_CGCM model predictions are obvious, there are still some areas where the correlation index is high to 0.6, such as the western equatorial Pacific at u₂₀₀, the northern equatorial Pacific at v₂₀₀, the central equatorial Pacific at u850, the central North Pacific at v₈₅₀, some area around New Zealand at H₅₀₀, and so on. The total amount of grids where the positive correlations reach or exceed 95% statistical confidence is counted. For u₂₀₀ and u₈₅₀ there are more correlated grids, and correlated grids amount for H₅₀₀ is the smallest. An experiment is done using the summer precipitation index in the mid lower reaches of the Yangtze which is one of the 15 areas divided by climate characteristic in China. Some grids data are chosen where the correlations (between the precipitation index and NCEP, between the precipitation index and model products) are both positive, reaching or exceeding 95% confidence at the same time. With the chosen data from NCC_CGCM, the regional precipitation index is predicted by EOF downscaling method from 2003 to 2007, getting an accuracy of 80%. The precipitation forecast result got by downscaling with chosen data from the model proves better than those with the model and EOF downscaling with only H₅₀₀ product of CGCM for the mid lower reaches of the Yangtze. The same downscaling is also run on the rest 14 areas from 2003 to 2007 but the accuracies are different. In Jiangnan and Inner Mongolia, the accuracies reach 80% too.