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Aerosol impact on the dynamics and microphysics of deep convective clouds

By A. Khain, D. Rosenfeld and A. Pokrovsky

Abstract

Mechanisms through which atmospheric aerosols affect cloud microphysics, dynamics and precipitation are investigated using a spectral microphysics two-dimensional cloud model. A significant effect of aerosols on cloud microphysics and dynamics has been found. Maritime aerosols lead to a rapid formation of raindrops that fall down through cloud updraughts increasing the loading in the lower part of a cloud. This is, supposedly, one of the reasons for comparatively low updraughts in maritime convective clouds. An increase in the concentration of small cloud condensation nuclei (CCN) leads to the formation of a large number of small droplets with a low collision rate, resulting in a time delay of raindrop formation. Such a delay prevents a decrease in the vertical velocity caused by the falling raindrops and thus increases the duration of the diffusion droplet growth stage, increasing latent heat release by condensation. The additional water that rises to the freezing level increases latent heat release by freezing. As a result, clouds developing in continental-type aerosol tend to have larger vertical velocities and to attain higher levels. The results show that a decrease in precipitation efficiency of single cumulus clouds arising in micro-physically continental air is attributable to a greater loss of the precipitating mass due to a greater sublimation of ice and evaporation of drops while they are falling from higher levels through a deep layer of dry air outside cloud updraughts. By affecting precipitation, atmospheric aerosols influence the net heating of the atmosphere

Year: 2005
DOI identifier: 10.1256/qj.04.62
OAI identifier: oai:CiteSeerX.psu:10.1.1.463.8548
Provided by: CiteSeerX
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