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Comparison of methods for deriving aerosol asymmetry parameter
Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA
Global Monitoring Division, NOAA Earth System Research Laboratory, Boulder, Colorado, USA
Visiting Scientist at Global Monitoring Division, NOAA Earth System Research Laboratory, Boulder, Colorado, USA
Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA
Global Monitoring Division, NOAA Earth System Research Laboratory, Boulder, Colorado, USA
Desert Research Institute, Reno, Nevada, USA
Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA
Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA
Department of Atmospheric Sciences, Texas A&M University, College Station, Texas, USA
Department of Atmospheric Sciences, Texas A&M University, College Station, Texas, USA
Center for Interdisciplinary Remotely-Piloted Aircraft Studies, Naval Postgraduate School, Marina, California, USA
Bay Area Environmental Research Institute, Sonoma, California, USA
Brookhaven National Laboratory, Upton, New York, USA
Values for Mie-equivalent aerosol asymmetry parameter (g) were derived using a variety of methods from the large suite of measurements (in situ and remote from surface and aircraft) made in Oklahoma during the 2003 aerosol Intensive Operations Period (IOP). Median values derived for dry asymmetry parameter at 550 nm ranged between 0.55 and 0.63 over all instruments and for all derivation methods, with the exception of one instrument which did not measure over the full size range of optically important aerosol. Median values for the “wet” asymmetry parameter (i.e., asymmetry parameter at humidity conditions closer to ambient) were between 0.59 and 0.72. Values for g derived for surface and airborne in situ measurements were highly correlated, but in situ and remote sensing measurements both at the surface and aloft did not agree as well because of vertical inhomogeneity of the aerosol. Radiative forcing calculations suggest that a 10% decrease in g would result in a 19% reduction in top of atmosphere radiative forcing for the conditions observed during the IOP. Comparison of the different methods for deriving g suggests that in computing the asymmetry parameter, aerosol size is the most important parameter to measure; composition is less important except for how it influences the hygroscopic growth (i.e., size) of particles.
Received 21 December 2004; accepted 7 June 2005; published 21 January 2006.
Citation: (2006), Comparison of methods for deriving aerosol asymmetry parameter, J. Geophys. Res., 111, D05S04, doi:10.1029/2004JD005734.
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