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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. D23, 8662, doi:10.1029/2002JD003066, 2003

Influence of relative humidity on aerosol radiative forcing: An ACE-Asia experiment perspective

Krzysztof M. Markowicz

Institute of Geophysics, University of Warsaw, Warsaw, Poland


Piotr J. Flatau

Naval Research Laboratory, Monterey, California, USA
Center for Atmospheric Sciences, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA


P. K. Quinn

Pacific Marine Environmental Laboratory, NOAA, Seattle, Washington, USA
Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, Seattle, Washington, USA


Christian M. Carrico

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


M. K. Flatau

Naval Research Laboratory, Monterey, California, USA


A. M. Vogelmann

Center for Atmospheric Sciences, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA


David Bates

Physics Department, University of Miami, Coral Gables, Florida, USA


M. Liu

Naval Research Laboratory, Monterey, California, USA


Mark J. Rood

Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA


Abstract

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.

Index Terms: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 1640 Global Change: Remote sensing; 3307 Meteorology and Atmospheric Dynamics: Boundary layer processes; 3359 Meteorology and Atmospheric Dynamics: Radiative processes.

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Citation: Markowicz, K. M., P. J. Flatau, P. K. Quinn, C. M. Carrico, M. K. Flatau, A. M. Vogelmann, D. Bates, M. Liu, and M. J. Rood (2003), Influence of relative humidity on aerosol radiative forcing: An ACE-Asia experiment perspective, J. Geophys. Res., 108(D23), 8662, doi:10.1029/2002JD003066.