Meteorological aspects of the atypical seasonal lightning distribution at the Gaisberg tower

Abstract

The seasonal lightning distribution at the Gaisberg tower in Austria is very different from the distribution observed in a circular ring with a radius of 2 to 10 km around the tower. The distribution in the circular ring shows the typical peak during the convective season. In contrast, we find a bimodal distribution with a peak in early spring and late fall at the tower. By selecting two cases representing these two situations, the differences in the meteorological setting are discussed.Lightning events observed solely at the Gaisberg tower are characterized by strong horizontal winds in the lower layers of the atmosphere from the northwest sector. This direction represents the open window from the Gaisberg towards the foreland, meaning there are no mountains upstream, and the flow can reach the Gaisberg unhindered. Cases of this type occur mainly during the cold season but are not limited to it.In contrast, lightning events at the tower and in its vicinity are typical for convective events with low horizontal wind speed in the lower layers and occur mainly during the convective season.