Orographically-induced deep convection over the Black Forest mountains during COPS

During the COPS campaign in summer 2007 deep convection was observed on July 15 (IOP 8b). The convection is restricted to the Black Forest mountains area. The data analysis reveals that the convection is triggered by different mechanisms. (i) Due to a shallow high pressure system which is situated to the east of the Black Forest and a trough which approaches from the west towards the investigation area, a convergence zone establishes in between. (ii) High insolation favours the development of slope and valley winds and high evapotranspiration results in the increase of moisture in the boundary layer. The thermally driven circulation systems result in a convergence line along the mountain crest of the Black Forest. (iii) Both convergence lines optimally superimpose when the synoptic scale system reaches the Black Forest. At this time a strong upward motion can be observed above the mountain crest for about one hour, as obvious from the wind lidar data. This upward motion penetrates through the CBL-capping and upper level inversion and transports moist air from the Rhine valley into the free atmosphere. Consequently, CAPE is released and deep convection develops with heavy showers. The different states of the evolution of deep convection will be demonstrated based on the dense surface, remote sensing and profiling network of COPS.