低纬高原一次飑线过程的地闪演变特征分析

利用雷电定位资料、多普勒雷达资料和FY-2E红外卫星资料,分析了滇西南一次典型飑线过程的地闪变化特征。结果表明,这是一次由切变线云带内的对流单体与台风外围对流单体合并形成的典型飑线过程。在飑线发展初期,负地闪占主导地位,地闪频数在波动中缓慢增加;在飑线成熟阶段,地闪频数较高,负地闪频数达到最大峰值前10～15min,正地闪出现最大峰值;在飑线减弱阶段,地闪频数急速下降,正地闪所占比例急剧增加,当正地闪所占比例超过地闪总数的8%以上时,地闪活动开始呈减弱特征。负地闪主要发生在强对流区(>40dBz),对应着径向速度场上的辐合区,密集的正地闪发生在飑线成熟阶段,对应着辐合区附近>40dBz的强回波区域,稀疏的正地闪发生在强回波外围的云砧或稳定性降水部位。在飑线整个发展阶段,-10℃,-20℃层高度上雷达回波强度的每一次跳跃变化都对应着地闪频数的跳跃发展,且-10℃和-20℃层高度上雷达回波强度总在地闪频数变化之前6～30min。负地闪集中出现在-92～-90℃和-76～-74℃的云区,而正地闪集中发生在-90～-60℃的云区。

Analysis on Lightning Activity Characteristic of a Squall Line System in Low-Latitude Plateau

The activity characteristics of cloud-to-ground(CG) lightning during a typical squall line system process in southwest Yunnan was analyzed based on the data from lightning detection system,Dopplar radar and satellite.The result showed that the typical squall line system process was caused by combination of convective clouds within the cloud band of shear line and the ones outside of typhoon.The negative CG flashes were in the leading position at the first developing stage of squall line system and the CG flash rates increased slowly with the fluctuation.The CG flash rate was higher at the mature stage of squall line system,and the peak time of positive CG was earlier 10~15 min than that of negative CG.The frequency of CG flashes rapidly declined with the increase of positive CG flash ratio at dissipating stage of squall line system.The CG flash activities started to diminish when the frequency of positive CG flashes was more than 8%.The negative CG flashes clustered in the intense echo region(> 40 dBz),which corresponded to the convergence area in radial velocity field from Doppler rader.The positive CG flashes clustered at the time of mature stage closely,which corresponded to the area of intense echo(> 40 dBz) beside convergence region,and sparse positive CG flashes were observed in the cloud anvil outside of the intense echo area,or in stable precipitation region.Every jumping change of the radar echo intensity at the heights with-10 ℃ and-20 ℃ corresponded to the jumping development of the frequency of CG flashes,and the jumping times of CG flash rate were always behind that of the radar echo intensity.To the TBB,the negative CG flashes clustered in the in-92~-90 ℃ and-76~-74 ℃ cloudy areas,while the positive CG flashes clustered in the-90~-60 ℃ cloudy areas.