一次苏皖龙卷的多普勒雷达分析及其成因探讨

Doppler Radar Analysis and a Discussion on a Tornado Occurring in Border of Jiangsu and Anhui Provinces

基于多普勒天气雷达、NCEP再分析资料等资料，分析了基本反射率因子等雷达产品。从天气形势、热力动力条件、急流耦合等方面研究了本次龙卷的成因。结果表明：①最强回波强度达到55～60dBz，而龙卷发生期间降水不大。基本速度图上出现正负速度对，表现出非常典型的龙卷特征；②龙卷涡旋特征（TVS）较为明显，其出现时间与实际龙卷时间大致相同。而且TVS所反映的龙卷路径与实际路径的方向、长度基本相当；③龙卷发生在梅雨的天气形势下，是由高空前倾槽所引发的。不稳定指标说明龙卷发生前大气处在很不稳定的状态；④在龙卷发生前后，温度平流等值线为鞍形场结构；⑤龙卷发生前低层暖平流明显。200hPa以上层为冷平流；伴随着最大反射率因子的升高、中气旋质心高度的猛烈抬升和中气旋底高的增加；存在高低空急流的耦合现象。

Based on Doppler weather radar data and re-analyzed data from NCEP, this paper analyzes radar products for parameters such as basic reflection and a tornado from aspects of weather situation, dynamic and thermal conditions, jet stream coupling. The results include （1） the strongest echo intensity reaches 55-60 dBz without too large amount of rainfall, a pair of positive and negative velocities appears on the map of basic velocity, with very typical features of tornado; （2） Tornadic Vortex Signature （TVS） is relatively obvious, with its occurring time appropriately compatible with the real tornado that happened, the path of tornado reflected from TVS is basically consistent with the direction, longevity of the actual tornado; （3） the real tornado happened under the situation of Meiyu season, caused by the forward trough of upper air; Shawalter index and K index and Convective Available Position Energy （CAPE） indicate that the atmosphere before the occurrence of tornado was in a very unsteady state; （4） during the course of tornado, temperature advection isotimic line took a structure of col field; （5） warm advection at low layer became apparent before the occurrence of tornado, with cold advection predominating above 200 hPa, and meanwhile with the utmost reflectivity increasing, and the height of medium cyclone increasing dramatically and the bottom height of medium cyclone increasing; the coupling jet streams were seen between upper and lower atmosphere.