12th Conference on Cloud Physics


The impact of cloud processing by trade-wind cumulus on the light scattering efficiency of aerosol particles

Justin R. Peter, University of Leeds, Leeds, United Kingdom; and A. M. Blyth, J. B. Jensen, and D. C. Thornton

Conserved thermodynamic tracers, wet equivalent potential temperature and total water mixing ratio (θq and Q respectively) are used to characterize sub-saturated air parcels in a cloudy trade-wind cumulus layer. A mixing diagram of {θq,Q} samples close to a cloud shows that sub-saturated air, sampled at a constant altitude in the cloud layer upwind and downwind of a cloud band, is composed of air parcels that have originated from two levels; near cloud base and a level in the free troposphere. The only manner in which air from the sub-cloud layer can make its way into the free troposphere is via convection and, therefore, contains cloud-processed air. The largest values of θq identify air that has most recently been detrained from cloud and experienced less mixing with environmental air than air parcels with lower θq. As such, parcels with larger θq are more indicative of the effect of cloud processing on the aerosol particle and SO2 concentration than parcels with a smaller θq. We stratify the aerosol size distribution, condensation nuclei concentrations, sulfur dioxide concentration and the aerosol extinction coefficient and mass extinction efficiency with θq. This enables physical interpretations about cloud processing of aerosol particles and SO2 to be inferred. Although there is evidence of mass addition of sulfate to aerosol particles and an observable modification of the aerosol size distribution, we find no modification of the aerosol extinction coefficient nor the aerosol mass extinction efficiency.

extended abstract  Extended Abstract (704K)

Poster Session 2, Cloud Physics Poster Session II
Wednesday, 12 July 2006, 5:00 PM-7:00 PM, Grand Terrace

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