一次华北暴雨过程的数值模拟及水汽螺旋度和水汽涡度收支应用分析

运用WRF模式对2009年8月发生在华北地区的一次暴雨过程进行了数值模拟,按照性质的不同对模拟降水进行了研究,还进行了湿度场试验,最后利用模式输出结果对水汽螺旋度和水汽涡度收支进行了诊断分析。结果表明,数值模式比较合理地再现了本次暴雨天气过程。显式降水在模拟的总降水量中占了很大的比重,但是在暴雨爆发初期,积云降水起了重要作用。对流层中层的水汽饱和程度对模拟降水性质及降水量大小有重要影响,显式降水一般发生在空气饱和程度较高的区域,而位势不稳定则是诱发积云降水的主要原因。对流层中低层水汽螺旋度的强度变化在一定程度上代表了降水系统的强弱变化,其高值区与强降水落区在出现的时间和空间上都存在较好的一致性。水汽涡度收支对于水汽涡度及水汽螺旋度的变化具有很好的指示意义,可以作为预报降水的一个动力指标。

NUMERICAL SIMULATION AND APPLICATION OF MOISTURE HELICITY AND MOISTURE VORTICITY BUDGET ON A RAINSTORM PROCESS OVER NORTH CHINA

Using the WRF model, a rainstorm over North China is numerically simulated. Analysis shows that the grid scale precipitation accounts a large proportion for total precipitation during the whole process while the cumulus convective precipitation only plays an important role at the beginning. The experiment on the humidity field indicates that saturation of the mid-lower troposphere has significant effect on the character and quantity of simulative precipitation. The grid scale precipitation often occurs in the saturated area, and cumulus convective precipitation is mainly induced by potential instability. The high-value area of moisture helicity in the mid-lower troposphere has good correlation with the precipitation area, and the moisture vortieity budget can be indicative of the variation of moisture vortieity and moisture helicity which can be used to forecast rainstorm.