Comparative Study Of Lightning Activities Between A Rainstorm Dominated By Warm Cloud Precipitation And A Supercell Cluster

Lightning activity and its associations with cloud structures during a rainstorm dominated by warm cloud precipitation were studied in Guangdong,China on 7 May 2017,using three-dimensional lightning location data,polarimetric radar observation data combined with wind-field and precipitation retrieval data.At the same time,the research above was compared with lightning activity and its spatio-temporal associations with cloud structures during a supercell cluster process in Oklahoma,United States on 10 May 2010?UTC?.Which deepens the understanding of the rules and characteristics of lightning activity during different types of thunderstorms and provides a reference for the analysis and application of lightning data and the study of lightning warning and forecast.The main results of the paper are as follows:?1?The overall convection and lightning activity during the rainstorm was weak.Its top height of the 40 d BZ echo did not exceed–10°C in most cases and the average lightning frequency was about 3 min^–1.The supercell cluster process had extremely strong convection.The top height of the 40 d BZ echo generally exceeded the–40°C layer,and its average lightning frequency was about 234 min^–1,which was much larger than that of the rainstorm process.The difference in charge structure between the rainstorm and the supercell cluster process resulted in different characteristics of their lightning activity.The tripolar charge structure during the rainstorm mainly generated negative cloud-ground flashes,and the proportion of positive cloud-ground flashes was only about 11%.After 04:00:00,the height of the charge region being significantly reduced,the lower positive charge region being weakened,and the upper positive charge region being more involved in the discharge increased the positive cloud-ground flash ratio from 3%to 29%.The macroscopic charge structure of the supercell cluster process showed inverted polarity,and its positive cloud-ground flash ratio was as high as 56.7%.At the same time,the proportion of cloud-ground flashes during the rainstorm was about 23%,while the proportion of cloud-ground flashes during the supercell cluster process was only about 1.07%.It is considered that the strong dynamic process of supercell may lead to the staggered distribution of large charge regions and small ones,which is not conducive to the occurrence of cloud-ground flash.?2?The correspondence between the main lightning active area and the precipitation area in the rainstorm process and the supercell cluster process was similar,but the reasons were different.The study found that high-frequency lightning activity in the two processes mainly corresponded to the areas with relatively weak precipitation on the ground.During the rainstorm,lightning discharge activity mainly occurred either at the edges of strong reflectivity columns or in the areas of weak reflectivity factors that were far away from the strong reflectivity columns,and the areas below them corresponded to relatively weak precipitation.In the early stage of the supercell process,lightning activity mainly occurred at the top of the inclined strong reflectivity column.Due to the characteristics of the structure's tilt,the corresponding precipitation below the top strong reflectivity was relatively small.In the mature stage of supercell,due to the large expansion of cloud area and the transport of a large number of charged particles,more accumulated lightning activity occurred in relatively weak precipitation areas.?3?The proportion of the main charged particles corresponding to the radar grid at the location of flash initiations and the lightning breakdown channel during the rainstorm and supercell cluster were significantly different.The hydrometeor predominantly associated with lightning discharges in rainstorm process was dry aggregated snow,while the proportion of graupel was low.The proportion of the grid boxes dominated by dry aggregated snow with Lightning Pulse Discharge Event?LPDE?and flash initiations were 81%and 87%,while the proportion of graupel were 9%and 8%.The hydrometeor predominantly associated with lightning discharges in the supercell cluster were dry aggregated snow and graupel,and the proportion of graupel was higher.The proportion of the grid boxes dominated by graupel with lightning sources and flash initiations was 43%and 49%,while the proportion of dry aggregated snow was 38%and 39%.?4?The significant difference in convective intensity between the rainstorm and the supercell cluster process also affects the difference in the correlation between lightning activity and precipitation.The overall convection in the rainstorm was weak,and the increase in convection will significantly affected the maximum rain rate and lightning frequency.Therefore,the total flash frequency and maximum rain rate had a good correlation in time.The overall convection in the supercell cluster process was very strong,and both precipitation and discharge were related to the cold cloud process,so there was a better correlation between the total flash frequency and precipitation.The rainstorm was dominated by warm cloud precipitation,making the amount of the corresponding rainfall per flash 10⁷ kg fl^–1,which was an order of magnitude higher than the 10⁶ kg fl^–1 of the supercell.?5?The correspondence between the main discharge area and the main electrification area of the rainstorm and the supercell cluster process may be different.The weak convection during the rainstorm made the electrification weak.At the same time,because the charged particles were transported outward,it was difficult to form a high-density charge region in the main electrification area that can effectively support frequent lightning discharges.And the charged particles in the weak convection area around the electrification area(analysis found that the concentration of lightning discharge during the rainstorm corresponds to the weak updraft and downdraft,and the LPDE and lightning initiation points in the vertical flow field velocity ranging from–4 to 4 m s^-1 accounted for 74%and 67%respectively)were more favorable to form high-density charge regions and supported more lightning discharge activities.Supercell was different.They had strong electrification efficiency in the areas with strong airflow?updraft in the early stage,entrainment in the later stage,and airflow shear area?.Although charged particles were also transported outward,the speed of the ice phase process and electrification was fast enough to consistently maintain the maximum charge density in the electrification area.From the density of the lightning sources,there was more frequent lightning discharge activity at the corresponding location.According to this,the research gives a conceptual model.