江西北部一次局地大暴雨过程分析

利用常规气象观测资料、区域加密自动站资料、GPS-PWV数据和NCEP 1°×1°再分析资料等,对2012年8月21日南昌短时大暴雨过程(8·21南昌大暴雨)进行分析,重点讨论了局地大暴雨的形成原因。结果表明:中纬度低压槽、东北方副高和东南方热带系统三者鼎立,致使江西北部聚集了高能量的不稳定大气,并在南昌附近产生局地强对流运动,导致了江西北部局地大暴雨的产生;地形抬升是8·21南昌大暴雨的直接诱因,由于梅岭山脉抬升作用,使不稳定大气上升到其自由对流高度以上,在梅岭山脉附近发展成中尺度气旋,气旋沿冷暖空气所形成的中尺度辐合线移到南昌市区附近,并在此地维持了3h;8·21南昌大暴雨是由多个强或特强的中小尺度降雨中心组成的,地面中尺度气旋、高CAPE值、高θ_(se)、强的水汽辐合等因素使得MCS得以长时间维持,使得中小尺度降雨中心在南昌市周边源源不断地生成发展。总结(8·21南昌大暴雨)流型配置,以此构造出这种弱西南气流条件下的预报概念模型,可以为预报员捕捉到此类局地大暴雨天气提供技术指导。

Analysis of a Local Heavy Rainstorm Process in Northern Jiangxi

Based on the conventional observation data, regional intensive automatic weather station data, GPS PWV data and NCEP 1°×1° reanalysis data, the short time heavy rainfall in Nanchang on 21August 2012 is analyzed. The discussion is focused on the causes of the local heavy rainstorm. The results show: The confrontation of a mid latitude trough, the Northeast Subtropical High, and a southeastern tropical system resulted in the accumulation of high energy unstable atmosphere and strong convective movement near Nanchang, and then led to the local rainstorm. The topographic uplift was a direct inducement of the rainstorm. Due to the uplifting effect of the Meiling Mountains, the unstable atmosphere ascended above its free convection height and developed into mesoscale cyclones near the Meiling Mountains. The cyclone moved along the mesoscale convergence line to the vicinity of Nanchang, and maintained for three hours. The rainstorm was composed of a number of strong or extra strong meso and micro scale rainfall centers. The ground mesoscale cyclone, high CAPE values, high and strong water vapor convergence made the MCSs maintained for a long time, which led to mesoscale rainfall centers repeatedly generated and developed around Nanchang. Summarizing the rainstorm flow pattern, we can construct the predictive conceptual model under the condition of weak southwest airflow and provide technical guidance for forecasters to capture such local heavy rainstorms.