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Influence of relative humidity on aerosol radiative forcing: An ACE-Asia experiment perspective
Institute of Geophysics, University of Warsaw, Warsaw, Poland
Naval Research Laboratory, Monterey, California, USA
Center for Atmospheric Sciences, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA
Pacific Marine Environmental Laboratory, NOAA, Seattle, Washington, USA
Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, Seattle, Washington, USA
Department of Atmospheric Science, Colorado State University, Ft. Collins, Colorado, USA
Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
Naval Research Laboratory, Monterey, California, USA
Center for Atmospheric Sciences, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA
Physics Department, University of Miami, Coral Gables, Florida, USA
Naval Research Laboratory, Monterey, California, USA
Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
We present direct radiometric observations of aerosol radiative forcing during the ACE-Asia experiment (March and April of 2001). The observational analysis is based on radiometer data obtained from the NOAA ship Ronald H. Brown, and shipboard measurements of the aerosol chemical and scattering properties are used to construct a model of the aerosol optical properties for use in radiative transfer calculations. The model is validated against the radiometric observations and is used to diagnose the aerosol and environmental factors that contribute to the observed forcings. The mean value of aerosol optical thickness observed during the ACE-Asia cruise over the Sea of Japan was 0.43 (±0.25) at 500 nm, while the single-scattering albedo was 0.95 (±0.03) at ambient relative humidity. We find a large correlation (r2 = 0.69) between single-scattering albedo and relative humidity. Aerosols caused a mean decrease in the diurnally averaged solar radiation of 26.1 W m−2 at the surface, while increasing the atmospheric solar absorption and top of atmosphere reflected solar radiation by 13.4 W m−2 and 12.7 W m−2, respectively. The mean surface aerosol forcing efficiency (forcing per unit optical depth) over the Sea of Japan was −60 W m−2 and is influenced by high values of relative humidity. We show that decreasing the relative humidity to 55% enhances the aerosol forcing efficiency by as much as 6–10 W m−2. This dependency on relative humidity has implications for comparisons of aerosol forcing efficiencies between different geographical locations.
Received 22 October 2002; accepted 3 March 2003; published 27 August 2003.
Citation: (2003), Influence of relative humidity on aerosol radiative forcing: An ACE-Asia experiment perspective, J. Geophys. Res., 108(D23), 8662, doi:10.1029/2002JD003066.
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