地形和水汽对“7.13”陕西暴雨影响的数值试验

Numerical Simulation of the Effect of Elevation and Water Vapor on“7. 13”Rainstorm in Shaanxi Province

应用WRF V3.5中尺度模式,对陕西省2013年7月12~13日的一次暴雨过程进行数值模拟,并设计了降低地形和减少水汽含量2个敏感性试验,探讨了地形和水汽对本次暴雨过程的影响。结果表明:(1)模式能较好地模拟出本次暴雨天气过程,反映出了主要雨带的形状,但模拟的降水量存在偏差,其可能原因是初始场不能合理反映大气实况;(2)嵌套区域d02的地形高度降低至原始高度的1/3后,107°E^109°E范围的散度垂直剖面呈辐合—辐散的双重结构,暴雨区上空中低层假相当位温梯度变大,垂直上升运动增强,进而改变了降水的强度和范围;(3)将初始场中暴雨区南面的水汽含量减少20%后,水汽通量散度极值中心值减少1/3,进而导致模拟区域的雨量减少了58%,表明偏南水汽的输送对本次暴雨雨量有显著增幅作用,暴雨过程中水汽聚集程度是判断暴雨过程雨量大小的关键因素之一。

Based on NCEP FNL reanalysis data with 1° × 1° spatial resolution and hourly precipitation in Yanchang,Huxian and Fuxian of Shaanxi Province,the typical rainstorm process which occurred in Shaanxi from 12 to 13 July 2013 was simulated by WRF V3. 5 meso- scale model. Combined with HYSPLIT track model,two sensitivity tests,which dropped the elevation of d02 area and reduced the water vapor content below 500 h Pa in southern rainstorm area in initial field,were designed to explore the effect of terrain and water vapor on the rainstorm. The results show that the WRF model can successfully simulate the process of heavy rain,and better depict the shapes of main rainbands. However,there are errors in simulating precipitation magnitude and rainfall region. When the elevation of d02 area is dropped to one- third,the zonal vertical section of divergence presents dual structure in 107°E- 109°E range,the gradients of pseudo- equivalent potential temperature at the middle and low level increase and the ascending motions enhance over the rainstorm region. And then change the intensity and range of rainfall. Furthermore,when the water vapor content decreased to 80% in the south of rainstorm region,the maximum moisture flux divergence reduced by one- third,and further led to the simulated precipitation decreasing by 58%. Thus,the water vapor transfer from the south has significant effect on the increase of rainfall. The collection of water vapor in the rainstorm process plays important role in rainfall.