ESRL/PSD Seminar Series

Abstract

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Aerosols that have the ability to influence cloud droplet formation can alter cloud microphysical properties and precipitation efficiency, location, and phase. Ice nuclei (IN) such as dust and biological aerosols can lead to early onset of ice formation that enhances riming and thus precipitation. Potential precipitation enhancement in regions such as California's Sierra Nevada has large implications on regional water supply, however, the magnitude of the effect of IN on precipitation is poorly understood. During the CalWater field campaign, chemical composition of precipitation residues was measured at Sugar Pine Dam in the Sierra Nevada. The fraction of dust and biological residues combined increased over time, from 20% in 2009 to 82% in 2011 of the total residues in all precipitation samples, in addition to increases in the total amount of precipitation (253 to 374 mm) and the frequency of snow storms (10% to 36%). A higher incidence of Asian transport likely contributed to the high dust and biological fractions in 2011. Further, precipitation samples from several sites in Yosemite showed higher fractions of dust with increasing elevation. Additional satellite and aircraft platforms in 2011 afforded a comprehensive dataset from ground to air, exhibiting increased fractions of dust and biological particles present during colder cloud temperatures and higher fractions of ice in-cloud. Observational data from CalWater will be used to evaluate model predictions of precipitation patterns in the Sierra Nevada. The overarching goal is to better understand aerosol-cloud-precipitation interactions and the impacts of aerosols on California's water supply during winter storms.

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