Observation of Convection Initiation Processes with a Suite of State-of-the-Art Research Instruments during COPS IOP8b

On 15 July 2007, an isolated thunderstorm was initiated above the Black Forest Mountains in South-Western Germany during the Intensive Observation Period (IOP) 8b of the Convective and Orographically induced Precipitation Study (COPS). Within this international field campaign, a large suite of airborne and ground-based research instruments was operated in a region covering the Vosges and Black Forest mountains and the Rhine Valley in between. e.g., the pre-convective atmosphere was sampled by a suite of different lidar systems to analyse the variability of moisture, wind, and temperature with high temporal and spatial resolution. The research systems were combined with dense networks of meteorological stations. The COPS measurements give detailed insight into the atmospheric processes which took place on this day in the region and their relation to the initiation of deep convection and form an excellent verification data set for case studies with numerical weather prediction models. Sensible and latent heat transport into the boundary layer, circulation systems in the mountains, forming of ABL height variations in the region, development of clouds and related latent heat release, overcoming convective inhibition and capping lids; the model representation of the chain of processes leading to CI can be verified step by step which is essential in order to confirm that the model shows the right results for the right reasons. We found that differences in the moisture field are responsible for the difference found over the Black Forest Mountain (isolated precipitating cells) and over the Vosges mountains (only shallow non-precipitating convection) but the moisture field alone cannot explain the timing and location of CI in this case. Sufficient moisture was uplifted only by convergence which was caused by interplay of smaller-scale thermal flows and channelling of larger-scale flows. Capping temperature lids inhibit the updrafts in the convergence zones which were formed until favourable conditions combine and deep convection is initiated.