Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 9 3 2009 10.5194/acpd-9-11367-2009 http://www.atmos-chem-phys-discuss.net/9/11367/2009/ http://www.atmos-chem-phys-discuss.net/9/11367/2009/acpd-9-11367-2009.html http://www.atmos-chem-phys-discuss.net/9/11367/2009/acpd-9-11367-2009.pdf 11367 11411 2009-05-07 Generation of free convection due to changes of the local circulation system R. Eigenmann rafael.eigenmann@uni-bayreuth.de S. Metzger T. Foken Department of Micrometeorology, University of Bayreuth, Bayreuth, Germany now at: Institute for Meteorology and Climate Research – Atmospheric Environmental Research (IMK-IFU), Karlsruhe Institut of Technology, Garmisch-Partenkirchen, Germany Eddy-covariance and Sodar/RASS experimental measurement data of the COPS (Convective and Orographically-induced Precipitation Study) field campaign 2007 are used to investigate the generation of near-ground free convection events in the Kinzig valley, Black Forest, Southwest Germany. The measured high-quality turbulent flux data revealed free convection to be induced in situations where high buoyancy fluxes and a simultaneously occurring wind speed collapse were present. The minimum in wind speed – observable by the Sodar measurements through the whole vertical extension of the valley atmosphere – is the consequence of a thermally-induced valley wind system, which changes its wind direction from down to up-valley winds in the morning hours. 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