Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 9 12 2009 10.5194/acp-9-4039-2009 http://www.atmos-chem-phys.net/9/4039/2009/ http://www.atmos-chem-phys.net/9/4039/2009/acp-9-4039-2009.html http://www.atmos-chem-phys.net/9/4039/2009/acp-9-4039-2009.pdf 4039 4052 2009-06-19 How important is the vertical structure for the representation of aerosol impacts on the diurnal cycle of marine stratocumulus? I. Sandu irina.sandu@zmaw.de J.-L. Brenguier O. Thouron B. Stevens CNRM-GAME, Meteo-France/CNRS, Toulouse, France Max Planck Institute for Meteorology, Hamburg, Germany University of California at Los Angeles, Los Angeles, CA, USA Large-Eddy Simulations (LES) are performed to examine the impact of hygroscopic aerosols on the diurnal cycle of marine stratocumulus clouds, under varying meteorological forcing conditions. When the cloud condensation nuclei concentration increase is sufficient to inhibit drizzle formation in the cloud layer, the precipitating and the non-precipitating cloud layers exhibit contrasting evolutions, with noticeable differences in liquid water path. Aerosol-induced modifications of the droplet sedimentation and drizzle precipitation result in noticeable changes of the entrainment velocity at cloud top, but also in significant changes of the vertical stratification in the boundary layer. This set of simulations is then used to evaluate whether a model which does not explicitly represent the effects of the interactions occurring within the boundary layer on its vertical stratification (i.e. such as a mixed-layer model) is capable of reproducing at least the sign, if not the amplitude, of these aerosol impacts on the liquid water path. 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