欧洲中期天气预报中心数值预报图的检验

为了对欧洲中期天气预报中心（ECMWF）数值预报图的优缺点有比较系统的了解，本文用1984年5月到1985年4月的一年北半球预报图资料，对各月平均误差分布情况及其季节变化特点作了统计分析。ECMWF数值预报图在35°—70°N之间的预报效果最好；在75°N 以北的高纬度地区，都是春、夏、秋三季500百帕高度的预报平均明显偏高，500—1000百帕厚度预报平均明显偏暖，其中又以夏季偏暖最显著，春、秋季次之（冬季则变为偏冷），年变化规律性明显；在30°N 以南地区夏秋两季都是500百帕预报明显偏低，厚度明显偏冷，最强偏冷中心位于青藏高原东南坡，冬春季则预报偏低和偏冷的程度减轻，年变化情况似与低纬度云雨量和热带低压活动的年变化大致相对应。青藏高原上空500百帕预报全年基本上都是负偏差，以夏季负偏差最大，春秋季减小，冬季趋于0，各月之间有近于正弦波型式的年变化规律性。把平均误差值与标准差相比较，可以看出低纬度地带（尤其是高原附近）是最需要也是最有利于进行系统性误差订正的地区。

A Study of Forecast Errors in ECMWF Operational Model

In order to have a better uderstanding on ECMWF model and make proper use in operation, the distribution of monthly mean errors and its seasonal variation is studied with one year data of the predicted charts from May 1984 to April 1985. ECMWF numerical forecast is best in middle latitude. In the area north of 75oN, 500 hPa height is forecasted too high and 500—1000 hPa thickness is too warm in spring, summer and autumn, especially in summer, but the latter becomes colder than that observed in winter. In the area south of 30oN, 500 hPa height forecast is too low and 500—1000 hPa thickness is too cold in summer and autumn, with the coldest error center situated on the southeast slope of Xizang Plateau; but in winter and spring, value of error is not so large as in summer and autumn. This seasonal variation seems to correspond with the cloud and precipitation amount or the activities of tropical low over there. Over the Xizang Plateau, the 500 hPa high forecast error is almost negative in every month of the year, with the largest negative value appeared in summer, but it approaches to zero in winter. Comparing the values of systematic error with standard deviation, we may find that in low latitude area, especially in the vicinity of Xizang Plateau, EC forecast charts need modification with systematic errors.