一次龙卷过程的WRF模拟及多普勒雷达反演风场研究

Characteristics Analysis of a Tornado Weather Using WRF Model and 4DVar Assimilation

利用中尺度WRF数值模式、多普勒雷达资料和4DVar风场反演算法,对2010年7月17日安徽砀山县、江苏省丰县等地发生的伴有龙卷的强对流风暴过程进行了综合分析。结果表明,此次龙卷风暴过程是在西太平洋副热带高压发展强盛,高空冷槽不断东移的大尺度环境背景下形成的;龙卷发生前大气环境具有较大的对流不稳定能量,低层存在大的风垂直切变和丰富的水汽供应;数值模拟显示,在安徽、江苏、山东三省交界处存在明显的风速辐合带,最大风速达15.5 m/s,且辐合区存在强的正涡度;在雷达回波径向速度图上,龙卷风暴中存在较强的中气旋(MC)和龙卷涡旋信号(TVS),尤其是在20:36,出现了东北—西南走向排列成线状的4个中气旋(MC)和一个龙卷涡旋信号(TVS);从雷达径向速度图上看到,TVS处可观测到正负速度对涡旋结构,正负速度差达64 m/s,说明TVS很强;用基于4DVar的风场反演方法可很好地反演出局地三维风场,并在MC、TVS出现的地方可反演出明显的小尺度涡旋结构,对龙卷的发生地点和流场结构有较好的描述。

Using WRF model,Doppler radar data and 4DVar assimilation method, we analyzed severe convective storms which were combined with tornadoes occurred in Dangshan of northern Anhui Province and Fengxian of northern Jiangsu Province on July 17, 2010. The weather diagnostic results show that the western Pacific subtropical high pressure system is strong, and high-altitude cold trough moves to the east. Before the tornado occurred there was a great convective instability energy in atmospheric environment, large wind vertical shear and abundant vapor supply in the lower level. We use the WRF model to simulate the mesoscale vortex under the large scale environmental conditions, the results show that there are mesoscale vortex systems in northern Anhui and Jiangsu Provinces. From the Doppler radar radial velocity, there are obvi- ous MCs （mesocyclones） and TVS （tornadic vortex signature）, and a positive and negative velocity structure, the speed difference can get 64m/s, We use a 4DVar assimilation method to achieve wind fields, and have a better description of the tornado point and the vortex wind field.