鲁西北一次持续性暴雨成因分析

利用地面自动气象站、NCEP 1°×1°和FY2E反演T_(BB)等资料,对2012年7月31日—8月1日发生在山东一次持续的区域性暴雨进行分析和研究。结果表明,(1)在副高稳定的形势下,低层切变线、地面冷锋是造成暴雨的主要天气系统。(2)低层锋生强迫激发了非地转垂直环流,上升气流加强,雨强增大,上升支的建立到强降水开始间隔约6 h。(3)暴雨区925 hPa湿斜压项在强降水时为负值,其增强应为低层锋生作用造成的。雨区范围和雨强随湿斜压项增强而增大。(4)对流单体的生成和加强影响降水落区和雨强,增强的单体合并时雨强最强。T_(BB)中心区位于低层切变线与锋面右侧,强降水位于两者之间。(5)地面辐合线与T_(BB)中心基本重合,辐合线左侧气旋性弯曲处与T_(BB)中心区后侧的等值线梯度大值区位置一致,强降水则出现在两者重叠处。(6)干线与辐合线是此次强降水的重要中尺度系统,干线始终落后于辐合线,其分布对暴雨落区有一定的指示意义。

Cause Analysis of a Continuous Rainstorm in Shandong Northwest

By using conventional data, as well as AWS(automatic weather stations) and NCEP1°× 1° and FY2E T_BB data, the causes of regional rainstorm in Shandong from July 31 to August 1 2012 are analyzed.The results indicate:(1)The low-level shear line and cold front were a major weather system of the rainstorm. The high-temperature and high humidity and strong southeast flow provided temperature and humidity conditions in the rainstorm area. (2)Low-level frontogenesis forced ageostrophic vertical circulation into effect. When the updraft was strengthened, precipitation intensity increased. The frontal zone and the southerly winds in 925 hPa which moved between north and south in the rainstorm area made the unstable energy released and rebuilt. (3)The moist baroclinic items of the moist potential vorticity was negative value in 925 hPa during rainstorm,which should be attributed to the low-level baroclinic enhancement of frontogenesis. The area and intensity of rainstorm increased when the baroclinic items enhanced. (4) When the convective cells generated and strengthened,the precipitation area and intensity increased. T_BB center located in the right of the low-level shear line and the frontal surface, but the heavy precipitation center located in the area superimposed by the T_BB center and the low-level weather systems.(5) The area of the cyclonic crook in the left of the ground convergence line which was consistent with the large value area of contour behind the T_BB center was the heavy precipitation.(6) The mesoscale dryline and surface convergence line was the rainstorm mesoscale systems. The dryline which was significant for the area of rainstorm was always behind the convergence line.