engleski

Characteristics of lightning behavior in hailstorms and hail properties in storms with overshooting tops

Previous research showed that in most cases intensification of the storms’ updraft is followed by an increase in total flash rate. Rapidly growing flash rate increases the potential for severe weather, but doesn’t imply the development of severe weather phenomena itself. During severe thunderstorms CG lightning production seems to be decreasing, while significant increase in the number of IC flashes is registered. In the hailstorms, regions with a reduced number of lightning strokes can be detected. These regions are usually short lived and related to the wet hail growth which is not conducive to hydrometeor charging. 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 distribution, registered by LINET Lightning Detection Network, 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 cloud to ground (CG) and intra cloud (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. For cases with apparent OT, detailed analysis of lightning properties and physical properties of hailstones on the ground (number, diameter and kinetic energy) is made. In order to find possible typical differences, these parameters are compared with the same parameters in cases where OT was not apparent.

hailpad data; lightning; overshooting top; hail characteristics

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