东北冷涡背景下一次龙卷过程的观测分析

2012年6月12日在吉林省白城市洮北区发生一次龙卷过程 (简称“612”龙卷)，对此次龙卷过程天气形势和雷达资料分析结果表明:龙卷发生在高空冷涡的东南象限、中高空急流北侧、低空急流左侧的对流不稳定区域及地面较暖湿的环境中，大气对流参数计算结果显示龙卷过程低层 (0~1 km) 的垂直风切变较强 (为6.0×10-3s-1)，抬升凝结高度较低 (低于1 km)，且龙卷发生前对流有效位能较大。同时，龙卷过程超过50 dBZ的强核高度均在4 km以下，为低质心的对流系统，龙卷产生于一条带状回波与一近似团状回波合并加强后的强回波带中，并逐渐演变成“S”型，伴有“V”型缺口，中心最强值达61 dBZ。根据多普勒天气雷达导出产品并结合径向速度图反映出“612”龙卷是发生在以龙卷涡旋特征为主的尺度较小且垂直涡度较大 (约为3.65×10-2~3.83×10-2s-1) 的强对流风暴中，持续时间较短。

Observation of a Tornado in the Circulation Background of Northeast Cold Vortex

The synoptic situation and Doppler radar data of the tornado process of Taobei District of Baicheng city in Jilin Province on 12 June 2012 (referred as "612" tornado) are analyzed, results are as follows.The tornado process occurrs in the southeast quadrant of the upper cold vortex, and in the convective unstable region of the north of the upper-level jet and the left of the low-level jet, also, in a relatively warm and humid environment of the surface systems. The caculation of atmospheric convective parameters shows that strong vertical wind shear (no less than 6.0×10-3 s-1) occurs at low layer (0-1 km) and relatively low lifting condensation level (no more than 1 km) exists in the tornado process, and the convective available potential energy is large before the tornado occurs. As for the radar echo characteristics, the height of the strong core (no less than 50 dBZ) is below 4 km in the tornado event, making it a low centroid convective system. The tornado occurs in the strong echo zones where a banded echo with an approximate nodular echo join together, and it gradually evolves into an "S" type with "V" type gap, and the echo of the strongest center value reaches 61 dBZ. Using the Doppler radar derived products and the radial velocity map, tornado vortex signature (TVS) could be detected, indicating that "612" tornado occurs in strong convective storm with smaller-scale TVS and larger vertical vorticity (about 3.65×10-2 s-1-3.83×10-2 s-1), having short duration. TVS could be identified in advance before the tornado, so it is very useful for estimation and prediction of tornados.