中国西北地区夏季降水分区客观预报

本文在降水分区的基础上,对西北地区夏季降水进行预报。利用2007—2010年的6—8月T639资料和相应时段的实况资料,通过概率回归降水等级方案进行建模,对2011年6—8月进行了试报。结果表明:与单站建模预报相比,分区建模降水预报TS评分在各时效、各量级上均有提高,并且在空报和漏报上有较大减少,特别是中雨预报改善明显。分区建模比单站建模所选因子更丰富,利用了模式产品的有用信息,因此预报效果更好。分区建模降水预报与模式直接输出降水预报的对比分析表明:分区建模的降水预报效果优于模式直接输出降水预报,尤其小雨预报效果显著,中雨和大雨36 h和60 h预报的空报现象明显减少。

Regional Modeling Forecast of Precipitation in Summer in Northwest China

According to the statistics, 1/2-2/3 precipitation occurs in June-August in Northwest China. Objective precipitation forecast is a difficult problem in NWP products interpretation at present. Precipitation in Northwest China is relatively rare event for single station. It is difficult to develop stable forecast relationships for single station. The stations are combined into regions with specific equations developed for each region. These regions are developed based on climatology and geographic similarity. These forecast equations are then applied to any station within a region. Regional forecast mode is more stable than single-station forecast mode, because precipitation sample size is increased.Seven weather divisions for summer precipitation over Northwest China are developed through Rotated Empirical Orthogonal Function method (REOF), defined by the large contours of the seven REOF models. Objective precipitation forecast is based on probability regression precipitation categorical forecast. First processing original precipitation to 0-1 corresponding categories, and then developing forecast equations of different categories and calculate each criterions. In real forecasting , the categorical precipitation will be determined through the criterion and the probability forecast of that category. Based on the daily precipitation data of station and T639 NWP products During summer of 2007-2010 .Precipitation forecast modes over the Northwest were established. the present study concerns the area of Northwest; however, more specifically, this covers the domain (35°-50°N, 73°-110°E), which includes a total of 260 weather stations .Precipitation during summer of 2011 was forecasted, Analysis of forecast result indicates that regional method is better than a station method, especially for moderate rain. From the factor analysis, regional model selected factor is more abundant than the single station modeling, so regional model make a better prediction. Corresponding to model direct forecast , regional forecast result is better, It has an obvious advantage on light rain forecast.