TRMM Based-studies On Lightning, Radar Reflectivity, And Ice Scattering Of Severe Weathers

The electrical activity in thunderstorms is closely related to ice crystal, graupel, supercooled water and convective updraft, and consequently lightning data can give some information about the microphysical and dynamic process in thunderstorms. The Tropical Rainfall Measuring Mission (TRMM) satellite can provide synchronous observations on lightning activity, radar reflectivity and ice scattering, providing an opportunity to study the relationships between lightning activity and microphysical and dynamic parameters in severe weathers. In this thesis, the data from the precipitation radar (PR), lightning imaging sensor (LIS) and passive microwave imaging (TMI) have been used to investigate the characteristics of lightning activity, radar reflectivity and ice scattering in 46 tropical cyclones over the north western pacific and 9 squall lines over China, furtherly analyze the relationships between the occurrence of lightning flashes, and radar reflectivity and ice scattering. The conclusions are presented as following:Firstly, lightning flashes are more likely to occur in the weaker periods of tropical cyclones, comparing with the stronger periods. There are different spatial distributions of lightning activity in the different intense periods of tropical cyclones. The largest flash density occurs in eyewall region during tropical storm, severe typhoon and super severe typhoon periods, while it occurs in outer rainband region during other periods. As a whole, the precipitation systems in tropical cyclones are dominated by stratiform rain, and the ice scattering signature is weaker. Given the same radar reflectivity, lightning flashes are more likely to occur during typhoon and severe tropical storm periods, but a larger threshold of radar reflectivity is needed in super typhoon periods.Secondly, the analysis on the tropical cyclones whose intensity reach the level of typhoon shows that there is a peak of lightning density in eyewall regions, and the largest radar reflectivity and strongest ice scattering also appear in eyewall regions. Given the same height and cumulative frequency, the reflectivity in eyewall regions is 2-5 dBZ larger than that in the other regions. For the same brightness temperature or radar reflectivity, lightning flashes tend to occur more frequently in outer rainbands than elsewhere. Larger Radar reflectivity or ice scattering is needed for the occurrence of lightning in eyewall regions.Lastly, we examined the relationships between lightning activity, radar reflectivity and ice scattering in 9 squall lines over China. The results show that most lightning occur in convective regions, which contribute 82.9% of the total flashes.79% of the total flashes are located near the pixeles whose radar reflectivity is larger than 35 dBZ in 7 km altitude. The result from the studies of convective cells shows that lightning flashes often occur in the convective celles whose maximum radar reflectivity in 7 km altitude is larger than 35 dBZ, and the lapse rate of maximum radar reflectivity between 6 and 9 km altitude is lower than 15 dBZ. The vertical profile of the maximum radar reflectivity has capability to reveal flash rate and vertical development of convective cells. It is found that 81.5% of lightning flashes occur in the region with brightness temperature lower than 200 K. There is a close relationship between flash rate and ice precipitation content between 7-20 km altitude in thunderstorm cells, and the correlation coefficient is 0.72.