两次对流过程雷电预报的误差分析

Error Analysis of Lightning Forecast for Two Convective Storms

2014年6月17日和6月19日午后鄂西山地先后发生了两次对流过程,雷达回波出现了40 dBZ以上的对流特征,最强回波中心超过60 dBZ,全闪定位系统监测仅零星云闪,没有出现地闪。利用雷达、闪电、逐分钟地面观测等资料,对两次对流过程雷电预报的误差进行了分析,总结两种不同起电机制的对流概念模型。分析表明:(1)两次对流过程是在不同环流形势下发生的,午后热力条件是对流产生的直接影响因子,地面风场和温度场引起的中尺度扰动特征明显,动力和水汽条件偏弱。(2)对流尺度较小,呈直立状且结构松散,对流内部上升气流和环境场垂直风切变偏弱,-20℃高度以上≥40 dBZ回波所占比例较小,起电条件弱,这种类型的对流不利于电荷累积产生闪电。(3)在雷电预报过程中,雷达反射率强的对流并不意味着闪电发生概率大,判断对流过程中是否出现闪电,除考虑环境条件外,强的反射率必须超过0℃层等温线且持续时间较长、回波形态结构是否倾斜以及≥40 dBZ回波在-20℃高度以上的比例和维持时间是决定能否产生闪电的重要预警预报因子。

Two convective storms with≥60 dBZ radar echo and without cloud-to-ground(CG)lighting occurred on 17 and 19 June 2014 in western Hubei province.Based on Doppler weather radar,surface automatic station observation and lightning monitoring data,the environmental condition and radar echo structure of thunderstorm were analyzed.It shows that:(1)Two convective storms occurred in different circulation situations.Thermal conditions in the afternoon are the direct influencing factors,surface wind and temperature fields cause mesoscale disturbances,dynamic and water vapor conditions are weak.(2)Convective scale is small,vertical and loose,vertical wind shear of convective internal updraft and environmental field are weak,the proportion of echo with≥40 dBZ above-20℃ isotherm is small,this type of convection is not conducive to the accumulation of electrical charge to generate lightning.(3)The strong radar reflectivity convection does not mean there is a high probability of lightning occurrence.To judge whether lightning occurs in the process of convection,besides the environmental conditions should be considered,some other factors must be considered,including the long duration of strong reflectivity exceeding the 0℃layer,the tilted echo configuration,and the proportion and duration of echo with≥40 dBZ above-20℃.