NCC_CGCM产品对长江中下游夏季降水预报的释用

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

通过对1983—2002年国家气候中心NCC_CGCM季节预报模式的2月初始场的5个预测场(500 hPa高度场,200 hPa经向风、纬向风场,850 hPa经向风、纬向风场)与NCEP实况场的相关检验,指出模式预测与实况有一定差距,但也存在预报效果好的区域,其中预报效果最好的是200 hPa和850 hPa纬向风场,正相关达到95%信度的点数最多;500 hPa高度场正相关达到95%信度的点数最少;利用模式预报效果好的区域的预测值,对2003—2007年长江中下游区域夏季降水指数进行释用,预报准确率达到80%;对比模式在该地区的降水预报以及仅用模式高度场的解释预报发现,用挑选有用信息后的预报效果更好。该方法在全国其他14个区夏季降水的释用中,江南区和内蒙古区预报准确率也可达到80%。

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 u_（200）,the northern equatorial Pacific at v_（200）,the central equatorial Pacific at u_（850）,the central North Pacific at v_（850）,some area around New Zealand at H_（500）,and so on.The total amount of grids where the positive correlations reach or exceed 95%statistical confidence is counted.For u_（200） and u_（850） there are more correlated grids,and correlated grids amount for H_（500） 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 H_（500） 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.