Estimations of Ensemble Size for Numerical Climate Predictions
短期气候数值预报中的集合个数问题

Ensemble size has been estimated by using the hindcast results of 18-year(1980-1997), 28 members contained in each year. Taking extra-seasonal predictions of the summer rainfalls in China for example, the minimum ensemble size necessary to approach stable prediction result varies with area and year. The minimum ensemble size is 19 to 20 for the whole China, 10 or so for Southeast China, at least 20 for North China and Northeast China. In the year when the phenomenon of multi-equilibrium-state is found, the minimum ensemble size will be large. It is also shown that ensemble method is able to im- prove predictions for the area with positive skill, but not for the area with negative skill. In this case, correction of systematic errors is needed.