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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. D23, 8660, doi:10.1029/2002JD003233, 2003

Surface aerosol radiative forcing at Gosan during the ACE-Asia campaign

Brett C. Bush

Atmospheric Research Laboratory, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA


Francisco P. J. Valero

Atmospheric Research Laboratory, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA


Abstract

Surface radiation measurements were made at Gosan, Jeju, Republic of Korea, during the ACE-Asia field campaign aimed at assessing the impact of aerosols, specifically the “Asian yellow dust,” throughout the region. Downwelling total, direct, and diffuse radiative fluxes were measured in the total solar spectrum as well as near-infrared and visible portions of the spectrum. Aerosol optical depth measurements at 500 nm were also made using a scanning shadow band radiometer. Surface radiative forcing values were determined during clear-sky conditions made from 25 March to 4 May 2001. The diurnal forcing efficiency, determined by taking the slope of the best fit line through the flux versus optical depth plot, was found to be −73.0 ± 9.6, −35.8 ± 5.5, and − 42.2 ± 4.8 W m−2/τ500 for the total solar, near-infrared, and visible spectral regions. We also introduce a new radiative forcing parameter, the fractional forcing efficiency, defined to express the radiative forcing relative to the total energy incident at the top of the atmosphere. The fractional diurnal forcing efficiency at Gosan during ACE-Asia was −18.0 ± 2.3, −16.2 ± 2.4, and −26.7 ± 3.3%/τ500 for the same band passes, indicating that a larger percentage of the flux at visible wavelengths is radiatively forced compared to the total and near-infrared portions of the solar spectrum.

Received 27 November 2002; accepted 27 March 2003; published 26 August 2003.

Index Terms: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0360 Atmospheric Composition and Structure: Transmission and scattering of radiation; 0394 Atmospheric Composition and Structure: Instruments and techniques.

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Citation: Bush, B. C., and F. P. J. Valero (2003), Surface aerosol radiative forcing at Gosan during the ACE-Asia campaign, J. Geophys. Res., 108(D23), 8660, doi:10.1029/2002JD003233.