A Cloud-to-Ground Lightning Climatology for Romania

Abstract

Abstract The first study of the characteristics of cloud-to-ground (CG) lightning in Romania, based on the data recorded by the Romanian National Lightning Detection Network (RNLDN), is presented. The data, more than 1.75 million CG flashes, covers the entirety of Romania and were recorded between January 2003 and December 2005 and January and December 2007. The spatial analyses (total and positive flash density, the percentage of positive flashes, and negative and positive peak currents) were done with a resolution of 20 km. The average spatial distribution shows a maximum (3.06 flashes km−2 yr−1) over the south slopes of the central meridional Carpathians possibly associated with the Romanian Plain convergence zone. The mean monthly variation shows maximum CG lightning between May and September (98%) and minimum values in December and January. High values (>0.028 km−2 yr−1) for positive CG lightning density are observed in southwestern and central Romania. The monthly distribution of positive flashes shows a main maximum in May (25%) and a secondary maximum in August (23%), suggesting that positive flashes tend to occur earlier in the year than total flashes. The mean annual percentage of positive flashes has lower values at 1.3% in the central parts of the country. The percentage of positive CG flashes changes over the year from 1% in June to 19% in January. The monthly variation of the median first-strike peak currents has a maximum in winter and reaches a minimum in July, for both negative and positive currents. The mean diurnal cycle for total CG lightning flashes peaks between 1230 and 1430 UTC (2.2%) and shows a minimum between 0600 and 0800 UTC (0.3%).