Characteristics of Lightning 3D Distributions and Polarimetric Parameters in a Thunderstorm

To clarify the microphysical and kinematic characteristics of the thunderstorms, we studied the distributions of the three-dimensional VHF discharge, the polarimetric parameters and the vertical wind of the thunderstorms that occurred on 21 August 2013 in the Kanto Plain, Japan. From the observed polarimetric parameters near the lightning initiations, we found that the higher lightning initiation located at the graupel or ice crystal region and the lower lightning initiation located at planiform hydrometeor particle region on the early phase of the lightning activities. On the other hand, on the active phase of the lightning activities, the lightning didn't initiate at the region initiated on the early phase, but also at planiform hydrometeor particle region. Furthermore, we found the results that the lightning initiation above the freezing level were located at between the graupel and ice crystal region and the lightning initiation around the freezing level were located at between the rain and graupel region. These characteristics were described in the previous studies, but in this study we first investigated the relationship of the microphysical characteristics estimated by the polarimetric parameters and the lightning initiations for all lightning throughout the convective's life cycle. In addition, by the updraft analysis, we found the following mechanism of the lightning activities; 1) the strong updraft region appeared at the freezing level, 40 minutes before the first lightning occurred, and 2) the volume including the graupel increased at the bottom of the strong updraft region. 3) When the strong updraft region rose above and surged, the first lightning occurred around the graupel region. In the previous studies, the thresholds observing the reflectivity of 40dBZ at -10℃ have been suggested one of the best lightning predictor. Our results of polarimetric parameters and updraft analysis added the new informations to the lightning predictor. But we have to conduct more studies for other cases to find more sophisticated thresholds.