CATEGORIZED CORRECTION FORECAST FOR ACCUMULATIVE PRECIPITATION OF HEAVY RAINFALL PROCESSES BASED ON OPTIMAL PROBABILITY (OPPF) IN MEDIUM-EXTENDED-RANGE FORECAST TIME
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摘要: 采用ECMWF集合预报降水量资料和中国降水量观测资料,研发了基于最优概率的过程累计降水量分级订正预报(OPPF)技术,并在遵循总体技术思路的基础上设计出三种不同的OPPF计算方案(OPPF1、OPPF2、OPPF3),继而选用2015—2017年汛期(5—9月)中国91次区域性强降水过程进行回报试验和预报效果对比评估,结果表明:(1)在中期延伸期预报时效(96~360小时),对强降水和有无降水的预报效果,三种OPPF均明显优于集合平均(EMPF)和控制预报(CTPF);对中等以上或较强以上强度降水的预报效果,OPPF1和OPPF3明显优于CTPF、与EMPF基本接近。(2)三种OPPF相比,OPPF3的预报效果较OPPF1总体略胜一筹,两者均好于OPPF2。(3)预报效果存在明显的地域差异,南方地区强降水预报的TS评分明显大于北方地区,且OPPF3预报效果明显优于EMPF;在96~240小时预报时效,东北地区东部OPPF3强降水的预报效果也明显好于EMPF。Abstract: By taking the ensemble prediction data from ECMWF and the observations data of precipitation in China, the technology of categorized correction forecast for accumulative precipitation of heavy rainfall processes based on optimal probability (OPPF) is developed, and 3 calculation schemes of OPPF (namely OPPF1, OPPF2, and OPPF3) are designed according to overall technical route. Then the reforecast test is carried out for the accumulative precipitation of 91 heavy rainfall processes from May to September during 2015 to 2017 in China, and the forecast performance of the 3 OPPFs against that of ensemble mean (EMPF) and control number (CTPF) is evaluated and contrasted. The results show that: (1) In the medium-extended-range forecast time (96~360 h), the performance of the 3 OPPFs are better than that of EMPF and CTPF for heavy precipitation forecast and clear-rain forecast. The performance of OPPF1 and OPPF3 is better than that of CTPF and close to that of EMPF for precipitation above moderate intensity or larger intensity. (2) Among the 3 OPPFs, the forecast performance of OPPF3 is slightly better than that of OPPF1 in overall. Meanwhile the forecast performance of OPPF3 and OPPF1 is better than that of OPPF2. (3) There are obvious regional differences in forecast performances. TS in southern China are higher than in northern China, and the performance of OPPF3 for heavy precipitation is better than that of EMPF in southern China. During 96~240 h forecast time, the performance of OPPF3 for heavy precipitation is also better than that of EMPF in the eastern part of Northeast China.
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图 5 同图 4,但为累计降水量≥100 mm
表 1 OPPF1方案计算所得2015年7月29日12时起报的96~144小时强降水过程累计降水量各预报等级的最优概率阈值(OPCVk)。
k 1 2 3 4 5 6 Gk/mm 0.1 10 25 50 100 250 OPCVk/% 80.39 41.18 21.57 9.80 3.92 1.96 表 2 OPPF3方案计算所得2015年7月29日12时起报的96~144小时强降水过程累计降水量各预报等级的最优概率阈值(OPCVk)及其计算预报等级值(GkL)。
k 1 2 3 4 5 6 Gk/mm 0.1 10 25 50 100 250 OPCVk/% 31.37 45.10 27.45 23.53 9.80 3.92 GkL/mm 2.9 9.4 22.8 35 71 175 -
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