Difference in diurnal variation of lightning over Bulgaria and Black sea

The lightning activity over land (Bulgaria) and over maritime area (Black sea) during summer period (June, July, August) of 10 years is analyzed. Data for the location and time of detection of lightning provided from the ZEUS network operated by the National Observatory of Athens (NOA) are used. The results shows that summer-time flash density for each of the analyzed years is higher (between 1,5-3,5 times) over Bulgaria than over the Black sea, although the large differences in lightning activity during each year is established. However diurnal variation of flash density (at 3-h time interval) shows that during the night and morning hours lightning activity is higher over the Black sea than over Bulgaria (land), while between 9000 and 1800 UTC there is a predominant presence of lightning over land (Bulgaria). The analysis of spatial distribution of flashes at 3-hour time intervals reveals that the maximum of lightning activity during the afternoon (1200 UTC – 1500 UTC) correlates well with the location of mountains.