雷达资料的3DVAR和EnSRF直接同化方法对一次暴雨预报的影响分析

ANALYZING THE EFFECT OF 3DVAR AND ENSRF DIRECT ASSIMILATION OF RADAR DATA ON A HEAVY RAIN

利用合肥站雷达资料和NCEP再分析资料,采用WRF模式、WRF-3DVAR和WRF-En SRF同化系统设计了直接同化雷达径向风和反射率的试验,对2003年7月4—5日发生在江淮流域的一次梅雨锋暴雨过程进行数值模拟分析。结果表明:(1)同化雷达径向风资料可以增加暴雨区低层的扰动,增强对流运动,同时可以减少模拟的过量降水;(2)3DVAR同化方法对水平风场调整明显,同化反射率改进了模式中的微物理量和动力场,同时同化径向风和反射率可以更好地调整风场,改善模拟雷达回波带的强度和位置;(3)En SRF同化方法可以将更多小尺度的风场信息同化进入模式,单独同化反射率可以较准确预报出降水中心,同时同化径向风和反射率可以改进模拟雷达回波带的位置;(4)使用3DVAR和En SRF同化雷达径向风和反射率可以提高降水预报,改善雨带的范围,对降水中心位置和强度的预报也有改进。

The direct assimilation experiments of radial velocity and reflectivity are studied with the mesoscale numerical weather prediction model WRF V3.2,WRF-3DVAR V3.2 assimilation system and WRF-EnSRF assimilation system which is built in China.They are tested with a heavy rainfall process in the Mei-yu front that occurred in Yangtze River during 4 to 5 July 2003.NCEP reanalysis data and NextGeneration Weather Radar data of Hefei are used in these experiments.The results are shown as follows.（1） The direct assimilation of radial velocity can increase low-level disturbance,develop the convection and inhibit the excessive rainfall.（2） 3DVAR assimilation method can adjust the horizontal wind field significantly.Assimilating reflectivity can change the microphysical variables and dynamic field in the model.The wind and radar echo will be closer to the observation with the direct assimilation of radial velocity and reflectivity.（3） EnSRF assimilation method can assimilate small scale information of wind field to the model.Assimilating reflectivity can forecast the rainfall center accurately.Assimilating radial velocity and reflectivity can make the radar echo location well consistent with the observation.（4） The direct assimilation of radial velocity and reflectivity using 3DVAR and EnSRF can enhance the precipitation forecast and the scope of the rain belt greatly,which can improve the forecast of the location and intensity of the precipitation center at the same time.