Cooperative Institute for Research in Environmental Sciences

Science Rendezvous > 2009 Posters
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Measures of aerosol-cloud interactions and their uncertainties: A case study from the AMF Pt. Reyes deployment

Allison McComiskey¹,², Graham Feingold², Shelby Frisch³, Qilong Min⁴

¹Cooperative Institute for Research in Environmental Science, University of Colorado, Boulder / NOAA Earth System Research Laboratory, ²NOAA Earth System Research Laboratory, Boulder, CO, ³Cooperative Institute for Research in the Atmosphere, Colorado State University / NOAA Earth System Research Laboratory, ⁴Atmospheric Sciences Research Center, State University of New York, Albany

Measures of aerosol-cloud interactions (ACI), derived from a range of instruments and platforms, vary widely. As these measures are used in GCM parameterizations, understanding the causes and nature of this variability is essential to understanding and improving resulting uncertainty in calculated radiative forcing. Using data from a Department of Energy Atmospheric Radiation Measurement Program field deployment at Pt. Reyes, CA in 2005, we demonstrate the nature of aerosol-cloud interactions, specifically the first aerosol indirect effect, and variability in ACI measures for marine stratocumulus over the California coast. Variability in observed ACI is high, while attribution of this variability to physical processes and/or measurement uncertainties is unclear. Empirical measures of ACI, explored for California coastal stratocumulus show consistency among various ACI representations and ground-based measures that are consistent with in situ airborne measures. Variability in ACI is shown with dependence on (1) assumption of constant cloud liquid water, (2) methods for retrieving cloud drop number concentrations (3) particle size, and (4) updraft velocity. Presented in the context of local cloud radiative forcing (100% cloud cover), variability in ACI translates to a range in calculated forcing from ~ -3 to -9 W m^-2 for CA coastal stratocumulus. For a range of cloud liquid water and aerosol concentrations, this forcing ranges from ~ -3 to -10 W m^-2 for each 15% increment error in ACI.