CHARACTERISTICS OF LIGHTNING ACTIVITY IN DEEP CONVECTIVE CLOUDS WITH THE OVERSHOOTING TOPS

In this study characteristics of lightning activity, such as type and amplitude of lightning strokes in convective clouds with overshooting tops (OT), are analyzed. OTs are specific cloud-top signatures representing a strong updraft, which in some cases can penetrate through the tropopause region into the lower stratosphere. The focus was on the warm part of the year (May-September) during 2009. The study area covers a region from approximately 41°N 8°E to 49.5°N 24°E. Deep convective clouds with OTs were detected from the Meteosat 9 data, using a so called COMB method based on the infrared window (IRW, 10.8 μm) channel and the absorption channels of water vapor (WV, 6.2 μm) and ozone (O3, 9.7 μm) in form of brightness temperature differences (BTD). Locations and times of the detected OTs were compared to the distribution and types of the lightning strokes, provided by the Lightning Location System, a part of the International Lightning Detection Network in Europe (LINET). For each satellite pixel meeting the OT criteria, occurrence of lightning discharge was searched 5 min before and after the time of the scan, within the range of 0.05° from the pixel position. The results present the characteristics of lightning in the vicinity of the OTs which might give an idea about the connection between the occurrence of the strongest updraft, represented with the OT in the cloud and the change in the lightning activity

SYNOPTIC AND MESOSCALE ANALYSIS OF HAILSTORMS OVER CROATIA ON 22 AND 23 JUNE 2007

A case of severe convective development affecting Croatia on 22 and 23 June 2007 is analyzed by means of synoptic material, satellite, radar and lightning data as well as hailpad data and hail observations. The development occurred during the passage of a cold front in strong upper-level south-westerly flow, bringing warm and humid air from the West Mediterranean. The onset of convection was triggered by the orographic lifting on the islands and later on the Dinaric Alps. A supercell developing in the North Adriatic split into two cells due to strong vertical wind shear and veering of the wind in the lowest 3 km. The right-moving cell with cyclonic rotation was longer living and the left one died out. Large hail was reported along the path of the cell. Later on, convective cells developing over the continental part of Croatia were of lower intensity, but still bringing hail of the hazelnut size. Hailpad measurements and hail observations show the distribution of hail in time and give the information about the sizes of hailstones. Aladin meso-scale model performance is tested for the development in the North Adriatic, showing that the model could successfully reproduce the environment and the conditions for severe convective development, however underestimating the precipitation amount