Processes driving deep convection over complex terrain: a multi-scale analysis of observations from COPS IOP 9c

摘要

The ‘Convective and Orographically-induced Precipitation Study’ (COPS) analysesthe processes driving deep convection over complex terrain. Convection initiation(CI) is mainly not only expressed by a single process, but by a variety of them, whichinteract on different scales in time and space and finally can lead to deep convection.A study of such a case over inhomogeneous terrain is presented in this article. Datafrom the COPS network of stations are taken to identify the time and location of CI.Inmany cases this is not the same location as the first convective clouds, showers oreven thunderstorms. It is shown that the interaction of the CI processes onmultiplescales locally leads to either deep convection and severe storms or calm weather. Theboundary conditions between the different outcomes are narrow.During IOP 9c (20 July 2007), a mesoscale convective system (MCS) embedded ina surface low over eastern France propagated north-eastward and a gust front of theMCS reached the COPS area. During the passage of the gust front through the Rhinevalley, convective activity was significantly reduced. The gust front reached the slopeof the Black Forest, and the warm and humid air above the mountain range prior tothe gust front was lifted up to 2000mwithin a short time period. Within the air priorto the gust front aloft from the surface, CI started along a north–south orientedline above the crest. Due to insolation ahead of the gust front, a convergence linedeveloped. The interaction of local-scale orographic winds, the regional-scale gustfront, the mesoscale convergence line, and the synoptic-scale cold front led to asquall line. Finally, individual severe convective cells formed along the outer sectionof the synoptic-scale cold front.