engleski

Analysis of the convective activity and its synoptic background over central Mediterranean (Croatia)

Deep convective activity, identified by lightning measurements and associated favorablesynoptic conditions are analyzed. The focus was on the warm part of the year (April to October) during the period 2006 - 2010, over six sub-regions in Croatia. A convectively active day is defined as a day with at least ten lightning strikes over the target sub-region. The obtained dataset is used to determine the climatology of the frequency and regional distribution of convective days and their inter-month variability. The analysis shows that 56% of all examined days, i.e. every second day during warm part of the year, is a day with convective activity. Convectively most active sub- region is North Adriatic, with 62, 4% of all days in the analyzed sample. The areas eastward of 16°E exhibit a peak in convective activity in June, contrary to more western sub-regions that show a maximum later in the summer, from July to August. The average temporal characteristics such as typical duration, onset and cessation of convection are estimated as well. In all sub- regions, the convective activity begins in the early afternoon and ends mostly in the evening. Nocturnal convection occurs more frequently along the Adriatic coast. In the second part, the dominant large-scale weather types and upper-level flow regimes, corresponding to the convectively active days, were determined using surface and upper-levels pressure fields. The lightning flashes are frequently detected in the non- gradient pressure field (23%), in the cyclone center (18%), in the leading (15%) and in the rear (12%) parts of the cyclone, as well as in the front part of a trough (11%). The southwesterly upper-level flow represents the most common flow regime (38%) in the days with convective activity. Slightly less, the northeasterly flow occurs with a frequency around 23% and the northwesterly flow in 18% of all selected days.

lightning; convection; weather types; upper-level flow regimes

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