Impact de l'aérosol sur le cycle de vie des nuages de couche limite

Abstract : Anthropogenic aerosols may have a noticeable impact on the life cycle of boundary layer clouds, via their effects on radiation and precipitation efficiency. It is however difficult to document such impacts from observations. The interactions between aerosol particles and the dynamics of boundary layer cloud systems (typically marine stratocumulus) have therefore been explored with high resolution numerical models (LES), that now include detailed parameterizations of turbulence, radiative transfer and microphysics. In this study, the focus is on the coupling between aerosol impacts on cloud microphysics and the diurnal cycle of stratocumulus clouds. LES simulations of a 36 hours cycle are performed with aerosol concentrations typical of pristine and polluted air masses, successively. Although the simulations start from the same initial state, they rapidly diverge. The increased concentration of cloud condensation nuclei yields to an increased droplet concentration, a reduction of the droplet sizes and the inhibition of the droplet sedimentation and precipitation formation. The liquid water content at cloud top hence increases and the cloud top entrainment is strengthened. Moreover, the absorption of solar radiation at cloud base is no longer balanced by the droplet and drizzle evaporation, and the decoupling of the cloud layer is reinforced. Overall, the polluted cloud layer is better coupled during the night and more decoupled during the day than its pristine counterpart. Measurable signatures of these impacts are identified to help at designing observational studies of aerosol impacts on the dynamics on boundary layer clouds.
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Submitted on : Friday, February 15, 2008 - 10:29:05 AM
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Irina Sandu. Impact de l'aérosol sur le cycle de vie des nuages de couche limite. Océan, Atmosphère. Université Paul Sabatier - Toulouse III, 2008. Français. ⟨tel-00256285⟩

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