Effects of aerosols on the properties of deep convective clouds Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/dz010s538

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  • Aerosols are tiny particles that serve as nuclei for cloud droplet and ice crystal formation. Increases in aerosol concentration lead to clouds with smaller but more numerous droplets. Some recent studies have found evidence that ice crystal size in deep convective clouds is also reduced by elevated aerosol concentrations. In this study, aerosol, cloud, and radiation data in the Clouds and Earth’s Radiant Energy System (CERES) Single Satellite Footprint (SSF) datastream are used to examine the findings of the earlier studies. Three years of CERES observations were used to survey the Earth for aerosols and deep convective clouds. A CERES field of view (FOV) was taken to contain a deep convective cloud if the 11-micron brightness temperature was below 210 K. To ensure that the cloud was in a region of active convection, the cloud had to be opaque at 11 microns. South America, Equatorial Africa, and the Northern Indian Ocean exhibited relatively high frequencies of deep convective clouds and contained high aerosol burdens. For each day, within each geographic region, 2° × 2° latitude × longitude regions that contained both deep convective clouds and aerosol retrievals were examined. If within a 10° × 10° region on a given day, two or more of the 2° × 2° regions were found, the differences in the properties of the clouds collocated with the large and small aerosol burdens were calculated. Differences in cloud properties were compared to simultaneous differences in aerosol burdens. This strategy ensured that the clouds and aerosols existed simultaneously and that the clouds with large aerosol burdens shared similar large-scale meteorology as those with small aerosol burdens. No link was found between the differences in aerosol burdens and deep convective cloud properties in any of the regions and seasons analyzed. Relationships among ice crystal size, cloud optical depth, and 11-micron brightness temperature were also investigated. Ice crystal diameter was found to decrease with decreasing cloud temperature. Likewise, cloud optical depth increased with decreasing cloud temperature. Such relationships among cloud properties and the inclusion of semitransparent clouds in earlier studies may explain why the findings of this study differ from those of earlier studies.
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