Bias Correction of Summer Extreme Precipitation Simulated by CWRF Model
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摘要: 基于1980—2015年6—8月CWRF模式(Climate-Weather Research and Forecasting model)14种方案的模拟结果和全国逐日降水观测资料,对比了Q-lin,Q-tri,RQ-lin,RQ-tri,SSP-lin和CDFt 6种误差订正方法对CWRF模式控制化方案(C1)模拟中国东部夏季日极端降水的订正效果,以CWRF模式14种方案日极端降水的模拟效果排名为基础,对比了模拟效果较好的4种方案集合、模拟较差的4种方案集合以及14种方案集合的订正效果,选出相对较好的订正方案进一步评估其成员集合后订正和成员分别订正后再集合的订正效果,结果表明:采用6种误差订正方法均可明显减少日极端降水模拟误差,其中RQ-lin方法订正效果最佳。CWRF模式对中国东部的极端降水指数均表现出较好的模拟能力,不同参数化集合方案得到14种方案成员先订正再集合与观测日极端降水平均值最为接近,研究结果对于改进模拟结果、提高其预测能力有重要应用价值。Abstract: The accurate forecast of extreme precipitation plays an important role in guiding the national economy and people's livelihood. The newly developed Climate-Weather Research and Forecasting model (CWRF) integrates a comprehensive ensemble of alterable parameterization schemes for each of the key physical processes, including surface (land, ocean), planetary boundary layer, cumulus (deep, shallow), microphysics, cloud, aerosol, and radiation. This facilitates the use of an optimized physics ensemble approach to improve weather and climate prediction. Evaluating the simulation performance and correcting the error can effectively improve the operational prediction level of extreme precipitation in CWRF model.Daily rainfall data simulated by CWRF model and observed at 2416 meteorological stations in China from June to August during 1980-2015 are used to compare correcting effects of Q-lin, Q-tri, RQ-lin, RQ-tri, SSP-lin and CDFt on extreme precipitation of control scheme simulated by CWRF in eastern China. Based on the simulation performance ranking of 14 parameterization schemes in CWRF model, effects of the top 4, the latter 4 and the ensemble of 14 parameterization schemes are compared. Correcting effects of two approaches are compared: Revising after the collection of members and revising before the collection of members. Main results show that the error of the extreme precipitation simulation of C1 scheme can be obviously reduced by using six error correction methods, among which the RQ-lin correction method is the best. Although there are great differences between parameterization schemes in the simulation of extreme precipitation index, CWRF model shows good ability for extreme precipitation index in eastern China. The first four parametric schemes with good extreme precipitation simulation ability are C13, C14, C12 and C1, while the C6, C4, C3 and C10 schemes perform worse, respectively. Different parameterization schemes are revised to ensure that it is the closest to the average value of observed extreme precipitation after each of 14 members of the parameterization scheme being revised. Results have important application value for improving outputs of model and improving its prediction ability.Error correction can only be used as a supplementary means to improve extreme precipitation prediction. The precision of model physical process and the improvement of model resolution are the key to improve extreme precipitation prediction.
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Key words:
- CWRF;
- extreme rainfall;
- simulation evaluation;
- error correction
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图 4 RQ-lin方法订正后不同方案集合的日极端降水平均值和观测值(a)观测,(b)C1,(c)C1,C12,C13和C14的集合,(d)C3,C4,C6和C10的集合,(e)C1~C14的集合
Fig. 4 Daily extreme precipitation mean for different parameterization schemes under RQ-lin revision and observation (a)observation, (b)C1, (c)sets of C1, C12, C13 and C14, (d)sets of C3, C4, C6 and C10, (e)sets of C1-C14
表 1 CWRF模式参数化方案组合
Table 1 Parameterization schemes of CWRF
方案 积云对流参数化 微物理过程参数化 C1 ECP & UW GSFCGCE C2 KFeta GSFCGCE C3 BMJ GSFCGCE C4 Grell GSFCGCE C5 NSAS GSFCGCE C6 Donner GSFCGCE C7 Emanuel GSFCGCE C8 ECP & UW Lin C9 ECP & UW WSM6 C10 ECP & UW Etamp-new C11 ECP & UW Thompson C12 ECP & UW Thompson-aero C13 ECP & UW Morrison C14 ECP & UW Morrison-aerosol 表 2 极端降水指数
Table 2 Extreme rainfall indices
指数名称 缩写 定义 单位 降水强度 SDII 总降水量/有雨日数 mm·d-1 暴雨日数 R50 日降水量不低于50 mm的日数 d 第95百分位降水量 P95 日降水量在第95百分位的值 mm 强降水量 R95P 日降水量大于第95百分位值的总降水量 mm 极端降水贡献率 R95T 超过第95百分位降水量之和占总降水量的百分率 % 表 3 验证时期CWRF模式C1方案模拟的日极端降水平均值经6种方法订正后与观测值的区域相关系数以及均方根误差
Table 3 Regional correlation coefficient and root mean square error of daily extreme precipitation mean from observation to revision of CWRF control scheme(C1) under 6 methods in validation period
订正方法 相关系数 均方根误差 Q-lin 0.81 10.29 Q-tri 0.78 11.64 RQ-lin 0.82 10.03 RQ-tri 0.80 10.75 SSP-lin 0.67 18.76 CDFt 0.73 15.77 表 4 14种方案模拟能力排名
Table 4 Ranking of simulation capabilities of 14 parameterization schemes
方案 泰勒评分 时间变率 综合 C1 3 8 4 C2 8 4 5 C3 10 13 12 C4 14 11 13 C5 11 2 8 C6 13 14 14 C7 12 7 10 C8 5 8 8 C9 4 8 5 C10 9 11 11 C11 6 6 5 C12 6 4 3 C13 1 1 1 C14 2 2 2 -
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