2013年7月7日苏皖龙卷环境场与雷达特征分析

以雷达探测资料为主,结合探空资料、天气图和地面灾情,对2013年7月7日苏皖2省交界处的龙卷进行了分析。结果表明：⑴龙卷是在低层有明显的风切变的有利形势下产生的,环境场具有较强的对流不稳定性、大的低层垂直风切变和较低的对流凝结高度。⑵反射率因子在60 dBZ左右;速度图上有正负速度对,低仰角的转动速度〉13 m·s-1;近地面相邻像素间速度差〉11 m·s-1,满足TVS速度差的最低阈值要求;天长龙卷和高邮龙卷都是发生在风暴发展极为旺盛后的1~2个体扫内,也发生在VIL比较大而下降到40~45 kg·m-2左右之时;天长龙卷发生在连续多个TVS之后,高邮龙卷发生在中气旋下降和TVS出现之时。风暴参数和TVS参数表征的指标越强越有利于龙卷的发生,影响范围也越大。⑶这次龙卷验证了出现龙卷的各项雷达识别指标：最强回波在6 km以下;有气旋性辐合,低仰角旋转速度〉13 m·s-1;既探测到中气旋也探测到TVS。⑷对经典龙卷概念模型进行简化,建立的简易模型证实了传统的龙卷风暴概念模型,给出了龙卷发生在TVS靠近上升气流一侧的解释。

Analysis on Environment Field and Radar Echoes Feature of a Tornado in Jiangsu and Anhui Provinces on 7 July 2013

Based on radar data,sounding data,weather maps and ground damage inquiry,a tornado storm which occurred on 7 July2013 in the junction of Jiangsu and Anhui Province was analyzed. The results are as follows：（ 1） The tornado occurred under the favorable situation with obvious wind shear at the low layer,and there were higher convective instable energy,bigger vertical wind shear at the low layer and lower convective condensation level in the environment field.（ 2） The reflectivity facter was about 60 dBZ,and there were positive and negative velocity on the velocity map,and the rotational speed of low elevation was greater than 13 m /s. The tornado occurred within 1-2 body scans after a storm developing mightily or when bigger VIL falled and reached about 40-45 kg·m-2. Tianchang tornado occurred after continuous multiple TVS,and Gaoyou tornado occurred when mesoscale cyclone declined and TVS occurred. The stronger the storm and TVS parameters were,the more tornado ocuurred,and its influence area was bigger.（ 3）The radar indicators of distinguishing tornado occurrence were verified through the tornado,for instance,the strongest echo was under the height of 6 km,there were cyclonic convergence and rotation speed of low elevation was more than 13 m /s,the mesoscale cyclonic and TVS were detected.（ 4） The traditional conceptual model of tornado was simplified,and the simple model explained the phenomenon about tornado occurring in TVS near the side of ascending flow.