冷空气影响台风暴雨的中尺度分析及数值模拟

Mesoscale analysis and numerical simulation of a typhoon rainstrom event affected by cold air

利用常规探测资料、NCEP/NCAR 1°×1°6h间隔的FNL再分析资料、NCEP GFS 0.5°×0.5°6h间隔资料、多普勒雷达和中尺度地面自动站资料,对2014年“麦德姆”台风暴雨对流系统的天气背景、触发机制以及生消演变过程进行分析,并用中尺度数值模式WRF进行侵入冷空气强度的数值敏感性试验。研究结果表明:(1)强降水发生在“麦德姆”北上变性的过程中,冷空气的侵入使得台风热力结构改变,台风外围的大气斜压性增强,层结更不稳定,有利于中尺度对流系统发生发展。(2)对流系统的触发首先是由边界层内冷空气侵入造成的,冷空气与暖空气的对峙使得江淮东部辐合加强、降水回波稳定少动。(3)数值敏感性试验结果表明,冷空气侵入使台风外围层结更加不稳定,有利于产生深厚的垂直运动,使中尺度对流系统的生命史长、强度强。若入侵冷空气过弱,对流系统中的垂直运动弱,对流强度弱;若入侵冷空气过强,虽然对流系统中能发展出强的垂直运动,但垂直运动维持的时间短,中尺度对流系统的生命史短,不利于产生持续性强降水。

Based on observation data,NCEP/NCAR(1°×1°)6 h interval FNL reanalysis data、NCEP GFS(0.5°×0.5°)6 h interval data,Doppler radar and mesoscale ground automatic station data,the environmental condition,triggering mechanism and the evolution of the convection system in the typhoon"Matmo"rainstorm in 2014 were analyzed.The numerical sensitivity experiments for intrusion of cold air intensity were also conducted.The results are as follows.(1)Rainstrom occurred during the process of typhoon transition.The invasion of cold air makes the thermal structure of the typhoon change,atmospheric baroclinic enhance in the periphery of typhoon and the stratification become more unstable,which is beneficial to the development of the mesoscale convective system.(2)The trigger of the convective system is caused by the intrusion of cold air in the boundary layer.The confrontation between cold air and warm air masses causes a strong convergence in the Eastern JiangHuai,which makes the precipitation echo persist.(3)The results of numerical sensitivity experiments show that the intrusion of cold air makes the outer region of the typhoon more statically unstable,which is conducive to the formation of deep vertical motion,prolonging and strengthening mesoscale convective systems.If cold air were too weak,the vertical motion in the convective system would be weak and so would the convection intensity.If cold air were too strong,although strong vertical motion could be developed in the convective system,the life span of the mesoscale convective system would be short,because the short time vertical motion could not be conducive to persistent strong precipitation.