11th Conference on Atmospheric Radiation and the 11th Conference on Cloud Physics

Monday, 3 June 2002: 9:15 AM
ACE-Asia aerosol forcing determined from aircraft and ground measurements
Francisco P. J. Valero, SIO/Univ. Of California, La Jolla, CA; and S. K. Pope, B. C. Bush, D. C. Marsden, A. Bucholtz, and Q. T. Nguyen
A suite of radiometers flown on the NCAR C-130 aircraft throughout the ACE-Asia experiment measured broadband and spectral fluxes. Identical instruments were placed in the zenith and nadir positions, allowing net flux and optical depth to be determined. The radiative forcing efficiency (aerosol forcing per unit optical depth) was determined below the aerosol layer, i.e. at an altitude of about 30 meters. This was measured in the spectral ranges 220 to 3910 nm (total solar forcing) and 680 to 3300 nm (near infrared) and in seven spectral channels covering contiguously the visible range from 400 to 700 nm. The radiative forcing was also measured above the lower aerosol layer, which yields an estimate of the forcing efficiency of the aerosol layer above (generally dust). The combination of forcing measurements above and below the lower aerosol layer (generally pollution aerosols) allows estimation of the solar heating in this layer.

At the surface comprehensive measurements of the solar insolation as well as the aerosol column optical depth were made. These measurements, in conjunction with aerosol-free model simulations, are used to determine the radiative forcing at the surface for the visible, near-infrared, and total solar spectral bandpasses. The predominant sources and compositions of the aerosols present in the measurement region located at Cheju Island, Republic of South Korea, ranged from anthropogenic "pollution" from large cities in China, Korea, and Japan to natural "yellow dust" transported from the Gobi desert area. The surface radiation measurements are used to characterize the overall climatic response to the combination and variability of the magnitude of the atmospheric aerosols. Analyses show that the diurnally averaged surface radiative forcing due to the aerosols is approximately -82.6 W/m2 per unit optical depth at 500 nm for the total solar broadband spectrum with a roughly equal contribution from the visible (-41.7 W/m2) and near-infrared (-44.0 W/m2) portions.

Supplementary URL: