2017-08-11内蒙赤峰EF4级山地多发龙卷灾调与成因分析

DAMAGE SURVEY AND ANALYSIS OF A MULTIPLE TORNADO EVENT OVER COMPLEX TERRAIN IN CHIFENG,INNER MONGOLIA ON 11 AUGUST 2017

2017年8月11日下午,三个EF4级龙卷袭击了内蒙古自治区赤峰市的地形复杂地区,造成5人死亡,58人受伤。这是1961年以来中国有记录的最强山地龙卷事件。首先给出了此次龙卷过程的灾情调查结果,接下来分析了此次龙卷母体风暴-龙卷超级单体产生的天气背景、关键环境参数以及多普勒天气雷达观测特征。本次龙卷事件发生在东北冷涡东南象限的地面锋前和干线向湿侧发展处,CAPE(对流有效位能)值为1800 J/kg,0~6 km风垂直切变为12.9 m/s,0~1 km风垂直切变达到10.8 m/s;同时,0~1 km相对风暴螺旋度达到67.3 m^(2)/s^(2),接近美国龙卷发生环境的中位数,有利于超级单体龙卷的发生。现场灾害调查发现,灾害路径具有多涡旋和不连续的特点,可能与当地的复杂地形有关。基于多普勒天气雷达相对径向速度图识别出三个龙卷涡旋特征(TVS),TVS径向速度差最大达到38 m/s。三个龙卷及对应TVS出自同一个超级单体的同一个中气旋,其中两个TVS出现时间重叠。

In the afternoon of 11 August 2017,three EF4 tornadoes occurred over the complex terrain in Chifeng,Inner Mongolia,China,causing five fatalities and 58 injuries.It is the most violent tornado event ever recorded on a hilly plateau in China since 1961.First,the results of a damage survey are presented in this work.Then,synoptic environments and key mesoscale parameters of the parent storm,a tornadic supercell,are analyzed,together with the signatures of tornadoes on a Doppler weather radar.This event occurred in the pre-frontal quadrant of the Northeast China Cold Vortex(NCCV)and on a bulge toward the moist side of a dry line associated with the NCCV.The CAPE(Convective Available Potential Energy)was 1800 J/kg.The vertical wind shears in the 0~6 km and 0~1 km layer were 12.9 m/s and 10.8 m/s,respectively.The 0~1 km storm relative helicity(SRH)reached 67.3 m^(2)/s^(2),which is close to the statistical median of U.S.climatology,indicating a storm environment favorable for tornadic supercells.Multiple vortices and an intermittent damage swath were observed via the Doppler weather radar,which was likely to result from the local complex terrain.The evolution of three radar-based tornado vortex signatures(TVS)were recognized,and the peak strength(maximum gate-to-gate azimuth radial velocity difference)reached 38 m/s.The three tornadoes and related TVS were generated from the same mesocyclone from a tornadic supercell,and two of them were overlapped in time.