METEOROLOGICAL SCIENCE AND TECHNOLOGY 1671-6345 2020 48 1 97 106 article 一種改進的降水臨近外推預報技術方法研究及效果檢驗 An Improved Method of Precipitation Nowcasting Extrapolation Forecasting and Its Verification 中尺度模式對于0~2 h的預報存在起轉問題,因此外推預報成為0~2 h臨近預報中不可或缺的技術方法。目前INCA(Integrated Nowcasting through Comprehensive Analysis System) 降水外推預報中,外推矢量擾動由外推矢量隨時間的變化確定,即相鄰時次外推矢量差確定,本文統計2017年7月 江淮地區(29°~35.5°N,114°~120°E)INCA系統相鄰10 min外推矢量偏差來代表外推矢量隨時間變化。若降水向東北方向移動,則外推矢量方向規定為東北方向。統計結果表明:①對于江淮地區,外推矢量以東北方向和西南方向偏差為主,外推矢量越大,其偏差的大小越大;②從外推矢量方向看,東北方向外推矢量占絕大多數(73%),可能是因為絕大多數降水發生在槽前形勢下,引導氣流為西南風。基于外推矢量偏差統計樣本,隨機生成多個符合外推矢量偏差分布的外推矢量擾動,得到多個不確定的外推矢量,將INCA確定性外推預報變為0~2 h降水外推集合預報,采用均方誤差(MSE)、TS評分、BIAS評分和Brier技巧評分等方法,對集合預報結果檢驗表明:隨著預報時效增加,集合預報比確定性預報的優勢更明顯。因此,考慮外推矢量的不確定性可以提高降水外推預報準確率。 Mesoscale models have the spinup problem in nowcasting (0 to 2 hour forecast), so extrapolation forecast has become an indispensable technical method for nowcasting. At present, the extrapolation vectors in INCA (Integrated Nowcasting through Comprehensive Analysis system) precipitation extrapolation prediction are deterministic and do not change with forecast time, which results in that the velocity and direction of precipitation movement do not change with the forecast time, which is inconsistent with the reality. It is necessary to consider the variations of extrapolation vectors with time and to make them as the disturbances of extrapolation vectors adding to deterministic extrapolation vectors. Extrapolated vector perturbations are determined by the variations of extrapolated vector with time, which is the deviation of extrapolated vectors at adjacent times. The adjacent 10minute extrapolated vector deviation during July 2017 of the INCA system is statistically calculated to represent the variation of extrapolated vectors with time. Extrapolation vectors are the current and future precipitation moving speed and direction. For easy understanding, if precipitation moves northeast, this paper stipulates that the direction of extrapolation vectors is northeast. The statistical results over the ChangjiangHuaihe Region demonstrate that the deviations are mainly in southwest and northeast. The larger the extrapolation velocities are, the greater the deviations velocities will be. Vast majority of precipitation occurs in front of troughs, so northeast extrapolation vectors account for 73%. 〖JP2〗Based on the statistical samples of extrapolated vector deviation, several extrapolated vector perturbations are generated randomly based on the distribution of extrapolated vector deviation, and several uncertain extrapolated vectors are obtained. The deterministic extrapolated prediction of INCA is changed to 0to2 hour extrapolated ensemble precipitation prediction. The ensemble forecast effects are verified by the Mean Square Error (MSE), TS score, BIAS score and Brier Skill score. The results demonstrate that the results of ensemble forecast are better than that of deterministic forecast with increasing forecast time. Therefore, the accuracy of precipitation extrapolation prediction can be improved by considering the variations of extrapolation vectors with time.〖JP〗 INCA;降水外推;集合預報;預報檢驗 INCA (Integrated Nowcasting through Comprehensive Analysis); precipitation extrapolation; ensemble forecast; verification 鄭淋淋,邱學興 ZHENG Linlin and QIU Xuexing /qxkj/article/abstract/20200114
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