一次暴雨过程的数值模拟和诊断分析

利用NCEP 1°×1°的6 h再分析格点资料和气象台站实测降水资料,采用WRF中尺度数值模式,对2008年7月23日发生在山东日照市的一次大暴雨过程进行了数值模拟和诊断分析。结果表明,此次大暴雨是在副热带高压、高空槽、西南低涡和切变线的共同作用下发生的;低层强烈的水汽输送和水汽辐合使暴雨区大气湿层迅速增厚,为暴雨的形成提供有利条件,水汽通量辐合中心与暴雨的落区有很好的对应关系;低层辐合高层辐散的配置有利于对流发展和低层水汽向高空输送;强烈垂直上升运动为暴雨发生提供了动力条件;700 hPa的垂直螺旋度与相应时次1 h降水存在很好的相关;强降水时段,暴雨区上空形成了从低层一直延伸到对流层顶层的正垂直螺旋度柱,暴雨中心的降水峰值正好出现在正螺旋度中心出现时段,垂直螺旋度中心的大小及变化一定程度上代表了降水系统的强弱和变化。

Numerical Simulation and Diagnostic Analysis of a Heavy Rainstorm

With 1°×1° NCEP reanalysis data and AWS rain data,a heavy rainstorm occurred in Rizhao on July 23rd of 2008 was simulated by the meso-scale numerical model(WRF) and diagnostic analysis of the heavy rainstorm are made by using WRF model outputs.The results showed that this heavy rainstorm was affected directly by the Western Pacific Subtropical High(WPSH) when it interacted with westerly trough in addition to the west-south vortex and the shear line of middle and lower layer.Strong transportation and convergence of water vapor resulted in the saturation vapour becoming deeper rapidly,which was helpful for the heavy rainstorm.Moreover,the center of the convergence of water vapor was corresponding to the location of the center of rainstorm.The high-level divergence and low-level convergence were favorable to the convection development and the water vapor transformation from low-level to high-level.Strong ascending motion can provide dynamical condition for the heavy rainfall.The vertical helicity at 700 hPa was closely related with the hourly precipitation.During the heavy rainfall period,a positive vertical helicity column was formed from the low level to top of troposphere,and the appearance of the peak value of precipitation was synchronized with that of the center of positive vertical helicity.