石家庄2012年夏季一次暴雨成因及可预报性分析

Analysis of one Unforecasted Rainstorm in 2012 in Shijiazhuang of Hebei Province

利用NCEP资料、雷达及地面加密自动站等资料,对2012年7月4日石家庄中部出现的一次漏报的暴雨天气过程,从天气形势、大尺度物理量场及逐小时加密自动站反演的物理量诊断等方面做了研究,并分析漏报原因。结果表明:受稳定副高的阻挡影响,西风槽在东移过程中向北移动,低层西南气流中产生暖性切变线,石家庄市位于切变线北部,短期预报暴雨难度大,切变线北部激发的强降水云团造成了石家庄的暴雨天气;物理量场假相当位温达到78℃,850 hPa比湿为14 g/kg,对暴雨预报有一定的指示意义;暴雨区位于TBB低值区边缘,雷达剖面质心高度低,属于热带降水型,以短历时强降水为主,地面辐合线出现在雷达回波产生后,在石家庄东部稳定维持0.5 h,对回波加强起正反馈作用;逐小时地面假相当位温、水汽压的空间分布与暴雨区有一定的对应关系,地面水汽辐合时降水强度加大,辐散使强度减弱。

In this paper the NCEP reanalysis data, radar and surface automatic meteorological stations data were used to analyze a heavy rainstorm process on July 4 in 2012 in Shijiazhuang which could＇ t be forecasted at that time. The results show that the main in- fluencing systems were upper trough and subtropical high, due to the block of the strong subtropical high, westerly trough moved to northeast, a warm shear line appeared in low level southwest airflow, and Shijiazhuang was located in north of shear line, the cloud cluster triggered by the warm shear line resulted in this rainstorm weather. The pseudo - equivalent potential temperature reached 78 ~C and specific humidity was 14 g/kg at the level of 850 hPa, which had the certain guidance significance for the rainstorm prediction. The torrential rain area located in the margin of the low value of TBB, and the rainstorm belongs to the tropical precipitation type. Sur- face convergence line maintained half hour in east of Shijiazhuang, which had positive role to strengthen radar echo. Certain correla- tions seem to exist between the hourly pseudo - equivalent potential temperature on the ground, the spatial distribution of vapor pressure and rainstorm area. Precipitation intensity increased when ground moisture convergence occured.