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降尺度技术在月降水预报中的应用
APPLICATION OF A NEW DOWNSCALING MODEL TO MONTHLY PRECIPITATION FORECAST
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摘要: 着重介绍月动力延伸数值预报模拟技巧较高的大气环流在局域降水方面的降尺度（downscaling）应用。克服动力降尺度和统计降尺度技术的缺点，从动力与统计相结合的角度，给出月尺度大气环流与局地降水之间的关系，该联系有清楚的动力学背景和天气学意义。120个月的历史实况资料回报试验证明了该关系的合理性。T63/NCC月动力延伸形势场集合预报进行中国降水的降尺度应用亦取得了较好的结果。Abstract: A relationship between monthly mean precipitation and monthly mean circulation represented by 500 hPa geo-potential height was given to combine dynamical and statistical approaches. The physical explanations of monthly mean circulation and precipitation were also presented. Statistical weights of each item of the relationship (the downscaling model) were derived from the monthly NCEP/NCAR reanalysis data (500 hPa) and China's observed precipitation data during the control period from January of 1951 to December of 1991. The hindcast test was conducted using those data from January of 1992 to December of 2001. The test indicates that the method (new model) has a high score skill for monthly mean precipitation forecast. Comparison of monthly forecast of precipitation amounts between the issued operational forecast and the new model using the 500 hPa height forecast obtained from T63/NCC GCM from January to June 2002 shows that the new model forecast has a higher score than the issued operational forecast result.
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图 2 1998年7月NCEP/ NCAR应用试验结果与实况 (均为降水距平百分率)
(a) 表示式 (1) 右端第一项的贡献，(b) 表示式 (1) 右端第二项的贡献，(c) 表示式 (1) 右端第三项的贡献，(d) 表示式 (1) 右端第四项的贡献，(e) 表示式 (1) 右端五项相加的结果，(f) 表示实况
表 1 2002年1~6月T63预报试验的降水预报与业务预报的评估对比
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