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夏季亚欧中高纬度环流的集合预报效果检验
The Ensemble Forecasting Verification on the Summer Eurasian Middle-high Latitude Circulation
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摘要: 使用NCEP集合预报资料, 对亚洲中高纬地区2003年6—8月500 hPa高度场的集合预报效果进行了检验。环流预报效果检验结果表明:预报时效大于5 d时, 集合平均预报明显优于单一预报; 使用相同模式分辨率时, 集合平均能将可用预报时效延长12 h以上, 达到7.5 d; 通过集合预报可获得真正意义的概率预报结果, 取得较单一高分辨率预报好的预报效果。阻塞过程的个例分析也表明集合平均的预报效果明显优于单一确定性预报; 特征等值线可反映集合成员的不一致信息和少数集合成员的异常表现, 以此为基础, 可估计分析对象出现与否的概率, 达到提高预报效果的目的。Abstract: The middle-range ensemble forecasting results of Eurasian middle-high latitude region (40°—80°N, 40°—150°E) in JJA 2003 are validated using NCEP EPS. The ACC and RMSE validation on the ensemble mean and deterministic forecasts shows that ensemble average forecasts are more efficient than single forecasts when the lead time is greater than 5 days. Under the same model resolution, ensemble average forecasts can extend the lead time of "usable forecasts" to more than 12 hours, even 7.5 days. The ROC analyses on the deterministic forecasts and ensemble probabilistic forecasts indicates that ensemble forecasting can provide the true probabilistic forecasts through the character of multi-members. The ensemble probabilistic forecasts have obvious advantages comparing to the single forecasts and are also better than increasing model resolution. The case study on the blocking system indicates that ensemble mean is better than single deterministic forecast. The characteristic isoline can reflect the disagreement among the ensemble members and the anomalous behavior in ensemble members. Based on those information, the probability of the target happening can be estimated, hence better forecast results can be achieved.
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图 1 2003年6—8月研究区域500 hPa高度场确定性预报检验结果
(a) 距平相关系数, (b) 均方根误差
Fig. 1 Verification resuslts of deterministic forecasts of 500 hPa geopotential height fields in the research region in JJA 2003
(a) ACC, (b) RMSE
图 2 2003年6—8月亚欧中高纬区域500 hPa高度场集合概率预报和确定性预报的ROC分析曲线预报时效分别为1 d (a), 3 d (b), 5 d (c), 10 d (d)
Fig. 2 ROC curve of ensemble probabilistic forecasts and deterministic forecasts of 500 hPa geopotential height fields in Eurasian middle-high latitude region in JJA 2003, the lead time is 1 d (a), 3 d (b), 5 d (c), 10 d (d)
图 3 2003年6—8月亚欧中高纬度地区500 hPa高度场集合概率预报和确定性预报的ROC面积
Fig. 3 ROC area of ensemble probabilistic forecasts and deterministic forecasts of 500 hPa geopotential height fields in Eurasian middle-high latitude region in JJA 2003
图 4 2003年6月24日00:00 500 hPa高度场不同预报时效实况与预报值之差 (单位:gpm)(a)7 d, (b)5 d, (c)3 d
(实线为R-M, 虚线为R-H)
Fig. 4 The difference between reality analyzing and forecast field of 500 hPa height at 00:00 on June 24, 2003(unit:gpm) the lead time is 7 d (a), 5 d (b), 3 d (c)
(solid line is R-M, dashed line is R-H)
图 5 2003年6月24日00:00 576 dagpm线不同时效预报和实况 (a)7 d, (b)5 d, (c)3 d
(粗实线为实况, 细实线为集合平均预报, 粗虚线为高分辨率预报, 细虚线为集合成员预报)
Fig. 5 Forecast and reality analyzing fields of the 576 dagpm isoline at 00:00 on June 24, 2003, the lead time is 7 d (a), 5 d (b), 3 d (c)
(strong solid line is reality analyzing field; thin solid line is ensemble average forecast; strong dashed line is high resolution forecast; thin dashed lines are the forecasts of ensemble members)
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