豫东龙卷的环境条件和雷达监测预警分析

Analysis of Environmental Conditions and Radar Monitoring Warning of Tornado in Eastern Henan

利用高空、地面、新一代天气雷达和NCEP/NCAR 1°×1°再分析等资料,详细分析了豫东平原地带4次龙卷的天气形势、环境条件和雷达监测特征,探讨了强降水过程中局地龙卷的诱发原因。结果表明:(1)4次龙卷多发生在高空分流辐散、中层中纬度槽前和副热带高压边缘西南暖湿气流形势下,低空急流、超低空急流和低涡、切变及地面低压辐合区是有利于暴雨过程中出现局地龙卷的主要影响系统。(2)单站探空参数特征为基本饱和的深厚湿层,温度垂直递减率较小,大气可降水量在5.6~6.7 cm,水汽条件非常充沛。对流有效位能差异较大,K指数多在30~43℃,-20℃、干球0℃(DBZ)、湿球0℃(WBZ)层高度均较高,而自由对流高度和抬升凝结高度低。龙卷发生前0~6 km、0~1 km垂直风切变分别为14~22 m·s^-1和12~14 m·s^-1。相似过程物理量合成豫东龙卷易发区位于代表热力、水汽关键物理量的异常大值区中。(3)雷达回波上龙卷多由大范围暴雨回波前沿强回波带上的微型超级单体产生,对应速度图上有自西南向东北方向移动的中气旋和龙卷涡旋特征TVS。中气旋和TVS顶高和旋转深度多在4 km以下,底高多在0.5 km以下。(4)中气旋对龙卷的监测率个例间差异较大,在29%~75%,提前预警的时间基本在30~50 min;而TVS对龙卷的监测率可达50%~100%,但提前时间较短,在0~18 min。最大切变值的大小除了与龙卷强度有关外,与监测距离也有很大关系。

Based on upper-air observation,ground observation,the CINRAD radar,NCEP/NCAR(1°×1°)reanalysis and other data,analyzed the weather situation,environmental conditions and radar monitoring characteristics of four tornado cases in Eastern Henan Plain in details,and discussed the causes of tornadoes during heavy precipitation.The results show that:(1)The four tornadoes mostly occurred in the high-level diffluence divergence,the middle midlatitude trough and the southwest warm and humid airflow at the edge of the subtropical high.Low-level jets,ultra-low-level jets and low-vortex,shear and ground low pressure convergence zone are the main influencing systems that facilitate the occurrence of local tornado during heavy rain.(2)The singlestation sounding parameter is characterized by a nearly saturated deep wet layer,a small vertical temperature decline rate,an atmospheric precipitation of 5.6~6.7 cm,and water vapor is abundant.The convective available potential energy is quite different,while the K index is mostly at 30~43°C.The height of-20℃layer,0℃drybulb temperature(DBZ)layer,and 0℃wet-bulb temperature(WBZ)layer are all higher,while the free convection level and lifting condensation level are low.Before tornadoes occurred,vertical wind shear of 0~6 km and 0~1 km is respectively 14~22 m·s^-1 and 12~14 m·s^-1.Physical quantity of the similar process synthesize the tornado-prone area in Eastern Henan is located in the abnormal large value area representing the key physical quantities of heat and water vapor.(3)On the radar echo maps,the tornado is mostly generated by the micro-super-cell on the strong echo band before the large-scale rainstorm echo,on the corresponding velocity maps,there are mesocyclones and tornadic vortex signatures(TVS)moving from the southwest to the northeast.The mesocyclones and TVS top height and rotation depth are mostly below 4km,and the bottom height is mostly below 0.5 km.(4)The monitoring rate of mesocyclone to tornado varies greatly from 29%to 75%,and the early warning time is basically 30~50 minutes.The TVS monitoring rate of the tornado can reach 50%~100%,but the advance time is shorter in 0~18 minutes.In addition to the strength of the tornado,the maximum shear value is also related to the monitoring distance.