梅雨锋暴雨中尺度对流系统触发和组织化的观测分析

Observational analysis of initiation and organization of meso-scale convective systems in a heavy rainfall event associated with Meiyu front

利用观测和NCEP再分析资料,对2015年6月26—28日江淮流域梅雨锋暴雨天气对流的触发和中尺度对流系统(MCS)的组织方式进行了分析。结果表明:梅雨锋附近发展的2个线状中尺度对流系统是暴雨的直接制造者。MCS2的发展有2种组织方式,26日夜间到27日凌晨,东西向雨带的不断后部建立和随后对流单体的列车效应是其发展的主要方式。27日凌晨到白天,初期新单体不断在线状MCS2的南缘触发,形成多个近乎平行的东北—西南向短雨带,后期梅雨锋锋面雨带从西部不断东移,经过强降水区;对流元有2种尺度的组织方式:新生对流单体沿着单个雨带向东北方向的列车效应以及东北—西南向雨带沿线状中尺度对流系统向东平移的"列车带"效应;持续的后部建立型和沿着同一路径不断的"列车带"效应使MCS2发展和维持。梅雨锋前不稳定空气的地形抬升和边界层辐合上升是初始对流的主要触发机制;26日夜间对流产生的冷池对对流的触发和MCS2的组织化及维持起重要作用,中尺度对流系统的组织特征和发生、发展受近地面环境场制约。

The initiation and organization of mesoscle convective systems（MCSs）that produced heavy rainfall over YangtzeHuaihe basin during 26-28 June 2015 are investigated based on diagnostic analysis of observations and NCEP FNL analysis product.The results show that two linear MCSs that developed to the south of the Meiyu front directly contributed to the heavy rainfall formation.There existed two types of organizational modes during the development of the MCSs.Repeated backbuilding and eastward echo training of convective cells were two major developing modes of the MCSs from the early night on 26 June to early morning on 27 June 2015.From the morning on 26 June till the daytime on 27 June,new cells continuously initiated in the southern end of the MCSs and formed several NE-SW oriented rainbands.Two scales of convective elements were found during the mature stage of the MCSs,i.e.the northeastward ＂echo training＂ of convective cells along individual rainbands and the eastward ＂band training＂ of the NE-SW oriented rainbands along the quasi-linear MCS.Continuous back-building and echo training of convective cells along the same path and ＂band training＂ of the NE-SW rainbands contributed to the development of the MCSs.Orographic lifting of the unstable air ahead of the Meiyu front and the boundary layer convergence were the major initiation mechanisms for convection.Cold pools played an important role for the initiation,organization and maintenance of the MCS.Note that the characteristics of organization and evolution of MCS were restricted by environmental background in the surface.