engleski

Lightning distribution during the hailstorms with the overshooting tops

In this work lightning characteristics are studied for ~ 40 cases of hail-producing thunderstorms occurring over Croatia in summer months (May to August), from 2008 to 2012. Lightning data were provided by the Lightning Location System, which is part of the International Lightning Detection Network in Europe (LINET). The LINET system detects total lightning discharge, but it also separately detects cloud to ground (CG), or intra cloud and cloud to cloud strokes (IC). Lightning distribution was compared to hail occurrences, based on data collected from a hail-pad polygon located in NW Croatia. The polygon, consisting of 150 hailpads, covers the area of app. 600 km2 with approximate distance between hailpads of up to 2 km. The results will show spatial and temporal characteristics of lightning distribution and polarity as well as portion of CG and IC lightning before, during and after the time of hail occurrence. Additionally, all studied hailstorms were checked for the appearance of the overshooting tops (OT) using a method based on SEVIRI brightness temperature differences and verified in high-resolution visible (HRV) images, where available. Satellite based OT detection method combines the criteria for the IRW brightness temperature and the criteria for two BTDs, WV-IRW and O3-IRW. All pixels with O3-IRW BTD larger than 13 K in the region where IRW brightness temperature is lower than 215 K and WV-IRW BTD larger than 4 K are characterized as OTs. Sharp increase in lightning activity and larger values of the electric current are evident at the time of the OT detections. At those times, lightnings occur well above the tropopause, being clearly related to the OT parts of the Cumulonimbus cloud. Lightning distribution during hailstorms with the OT, a manifestation of very strong updraft within the convective cloud, might give an idea about the connection between the occurrence of the strongest updraft in the cloud, hail development and the change in the lightning activity.

convection; lightning; overshooting tops; SEVIRI brightness temperature differences; hail characteristics

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