基于四维变分同化的“6·23”阜宁龙卷大涡模拟研究

Large-eddy simulations of the tornado over Funing on June 23 using a four-dimension variational data assimilation

应用WRF模式和四维变分同化方案(4DVar),进行2016年6月23日江苏省盐城市阜宁县EF4级超强龙卷大涡模拟研究。结果表明:NCEP/GFS预报场同化高频次地面观测和雷达风场资料能有效改进模式初始场,在阜宁附近模拟生成对流单体。在此基础上使用约100 m水平分辨率的大涡模拟,可以清晰模拟出超级单体的钩状回波和类龙卷涡旋结构。进一步分析模拟结果发现,对流有效位能和垂直风切变在天气尺度范围内均能达到有利于超级单体发生的阈值。有利于生成龙卷的高风暴相对螺旋度(SRH)集中在龙卷超级单体发生区域的风暴尺度范围内,且具有较好的指示性。尽管SRH的强度随模式分辨率有所提高,但其空间分布并无明显变化,在3 km水平分辨率网格已出现明显信号。

A simulation is produced for the June 23,2016 Funing(in Yancheng city,Jiangsu province)via WRF model and four-dimensional data variational assimilation.Results show that the first guess can be improved by assimilation of high-resolution surface and radar wind field observations from NCEP/GFS data,while convection cells are generated near Funing.Based on this,the simulation successfully produces hook echo and the tornado-like vortex structure when the large-eddy simulation is conducted on the 100-m grid.Furthermore,both convective available potential energy and vertical wind shear can reach the threshold value favorable for the occurrence of supercell in the synoptic scale.The high storm relative helicity(SRH)exhibits in the realm of parent supercell within a storm scale range,which is an indication of tornadogenesis.Although the intensity of SRH varies with resolution,its spatial distribution has not changed significantly,and signals are manifest using a horizontal grid spacing of 3 km.