两次台风衍生龙卷的环境背景和雷达特征对比分析

Contrastive analysis of two intense typhoon-tornado cases with synoptic and doppler weather radar data

利用ECMWF高分辨率再分析资料及广州多普勒天气雷达资料,对1522号台风"彩虹"外围衍生的广州番禺龙卷和1806号台风"艾云尼"外围衍生的广州南沙龙卷进行对比分析,同时还挑选了一个未发生龙卷的台风做外围环境参数对比。结果表明:两次强龙卷都发生在登陆台风的东北象限,中低空急流明显、低层辐合、高层辐散在珠江三角洲地区叠加是产生龙卷的有利天气背景。环境影响因子均表现为对流有效位能较大、低层风速较大、垂直风切变较强、抬升凝结高低较低、抬升指数较小、风暴相对螺旋度较大:相比之下,未发生龙卷的台风外围中低空急流依然明显,但其他环境影响因子大多数未达到发生龙卷的条件阈值。雷达反射率上均表现为一些超级单体特征,最强反射率均在59 dBZ以上,且低仰角都存在明显的速度对。由于"彩虹"龙卷过程的对流有效位能、中低层风速、低层风切变、抬升指数及中气旋强度等环境影响因子均明显强于"艾云尼"龙卷过程,导致其强度明显强于"艾云尼"龙卷。

Doppler weather radar data and ECMWF reanalysis data were used to analyze tornado events originated in the outside-region of 1522 typhoon“Mujigate”and 1806 typhoon“Ewiniar”contrastively,and a typhoon without tornado was selected for comparison as environmental parameters at the same time.Results show that two typhoon-tornado events both occur in the northeast quadrant of landfalling typhoons,with some advantageous environmental conditions including low-level convergence,upper-level divergence and superimposition of strong jet at mid and low level over the Pearl River Delta.Environmental parameters are shown to be relatively large convective available potential energy,strong wind at low level,strong deep low-level vertical wind shear,low condensation uplift height and large Storm Relative Helicity(SRH).In contrast,most of the environmental impact factors of typhoons without tornadoes didn t reach the conditional threshold for tornadoes except superimposition of strong jet at mid and low level over the Pearl River Delta.Radar reflectivity are shown to be supercell characteristic and the most strong reflectivity is all large than 59 dBZ,speed pair can be found at low-angle of altitude;but the environmental impact factors of typhoons just as convective available potential energy,low-level wind speed,low-level vertical wind shear,Lifted Index and the strength of mesocyclone caused by typhoon“Mujigate”are stronger obvious than typhoon“Ewiniar”,which cause typhoon-tornado strength by typhoon“Mujigate”stronger than typhoon“Ewiniar”.