Analysis of the convective activity and its synoptic background over Croatia

摘要

In this study, deep convective activity, identified by lightning measurements and associated fa vorable synoptic conditions, is analyzed. The focus was on the warm part of the year (April to October) during the period 2006-2009 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 distribu tion of convective days and their inter-month variability. The analysis shows that 56% of all ex amined days, i.e., every second day during the warm part of the year, are days with convective activity. The most convectively active sub-region is the 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 the more western sub-regions, which show a maximum later in the summer, from July to August. The average temporal characteristics, such as typical duration, onset and cessa tion of convection, are also estimated. 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 of this study, 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 center (18%), in the leading (15%) and in the rear (12%) parts of the cyclone; and 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 is the northeasterly flow, which occurs with a frequency of approximately 23%, and the northwesterly flow, with a frequency of 18% of all selected days.