Propagation characteristics of thunderstorms in southern Germany

摘要

The propagation of thunderstorms in southern Germany was investigated. The thunderstorms were observed by a lightning position system during the summer months of the years 1992 to 1996. On average every second day thunderstorms were observed anywhere in southern Germany. In general thunderstorms approach from westerly and south-westerly directions. The average speed is 13 m/s. No significant relation between the occurrence of thunderstorms and the large scale synoptic pattern described by the Grosswetterlagen (large scale weather pattern) was found. Thunderstorms were observed during almost all Grosswetterlagen. The reduction to 8 weather pattern based on the low-level flow in southern Germany showed that thunderstorms are likely when the flow has westerly directions (43%) or easterly directions (20%). Three distinct groups of different lightning patterns could be identified; stationary, moving thunderstorms and thunderstorm lines. The convective available potential energy (CAPE) and the wind shear were retrieved from the radio soundings from Muenchen and Stuttgart. On average CAPE was 583 J/kg for stationary, 701 J/kg for moving thunderstorms, and 876 J/kg for thunderstorm lines. The average bulk Richardson numbers are 152, 80 and 52 for stationary, moving thunderstorms and thunderstorm lines, respectively. The steering level was found to be at about 3 and 6 km m.s.l. However, it should be noted, that in most cases the soundings do not completely describe the local environment of thunderstorms, since radio soundings are only available twice a day. (orig.)