集合敏感性方法在高原涡和西南涡引发暴雨过程中的应用

An Ensemble Sensitivity Analysis of a Heavy Rainfall over Sichuan Basin under Interaction between Plateau Vortex and Southwest Vortex

基于欧洲中期天气预报中心ECMWF的集合预报和美国国家环境预报中心NCEP再分析等资料对2013年6月30日一次高原涡和西南涡作用下的四川盆地暴雨过程进行了分析。结果表明:(1)高原涡东移并和西南涡耦合加强导致了持续性暴雨的形成,集合预报的高原涡和西南涡之间的动力特征量(位势高度和涡度)的相关系数随时间逐步增大,表明两个低涡呈现出逐步耦合加强的特征;(2)集合敏感性分析可以用来揭示降水预报对于天气系统的敏感性,结合高度场和风场反映出低涡对暴雨的影响,此次过程暴雨对高原涡比西南涡更加敏感,在集合预报对西南涡预报不确定性较小的情况下,集合成员对高原涡的预报是影响降水强度和落区预报的关键因子,与实况更加接近的最优集合成员与控制预报相比,预报的高原涡强度更强,位置偏东;(3)30日,夜间降水量对低涡的动力特征量较白天更为敏感,主要是因为夜间暴雨是由高原涡和西南涡垂直耦合加强引发的,动力作用较明显,而白天的暴雨热力作用更加显著。

Based on the ECMWF ensemble data and NCEP 1°×1° reanalysis data,the characteristics of a heavy rainfall over the Sichuan Basin on June 30 in 2013 under interaction between Plateau Vortex（ PV） and Southwest Vortex（ SWV） are analyzed. Results showthat：（ 1） PV moved eastward coupling with SWV which caused persistent heavy rainfall. Correlation coefficients of dynamic parameters（ geopotential height and vorticity） between PV and SWV of ensemble forecast increased with time during the process indicating the characteristics of gradual coupling and intensifying of PV and SWV;（ 2） Ensemble sensitivity analysis can be used to reveal the sensitivity of rainfall to weather system and demonstrate the influence of vortex system on the heavy rainfall combined with geopotential height and wind fields. Heavy rainfall of this event was more sensitive to PV than SWV. When the forecast uncertainty of SWV of ensemble forecast was smaller,the forecast of PV was the key factor for forecasting of intensity and location of rainfall. Best ensemble members whose rainfall forecast was similar to the observed rainfall have stronger and easter location of PV compared to control member;（ 3） Heavy rainfall at night on June 30 was more sensitive to dynamic parameters of vortex systems than that in the day. Because heavy rainfall at night is caused by coupling of PV and SWV,which was characterized by more significant dynamic effect.In contrast,heavy rainfall in daytime was characterized by more significant thermodynamic effect.