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.