How important is the vertical structure for the representation of aerosol impacts on the diurnal cycle of marine stratocumulus? 1CNRM-GAME, Meteo-France/CNRS, Toulouse, France
2Max Planck Institute for Meteorology, Hamburg, Germany
3University of California at Los Angeles, Los Angeles, CA, USA
Received: 19 December 2008 – Published in Atmos. Chem. Phys. Discuss.: 02 March 2009 Abstract. 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. It is
shown that the evolution of the vertical structure is key to the responses we
simulate, and must be considered in bulk models that wish to predict the
impact of aerosol perturbations on the radiative properties of
stratocumulus-topped boundary layers.
Revised: 16 May 2009 – Accepted: 22 May 2009 – Published: 19 June 2009
Citation: Sandu, I., Brenguier, J.-L., Thouron, O., and Stevens, B.: How important is the vertical structure for the representation of aerosol impacts on the diurnal cycle of marine stratocumulus?, Atmos. Chem. Phys., 9, 4039-4052, doi:10.5194/acp-9-4039-2009, 2009.