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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. D13, 8474, doi:10.1029/2002JD002435, 2003

Estimates of the spectral aerosol single scattering albedo and aerosol radiative effects during SAFARI 2000

Robert W. Bergstrom

Bay Area Environmental Research Institute, Sonoma, California, USA


Peter Pilewskie

NASA Ames Research Center, Moffett Field, California, USA


Beat Schmid

Bay Area Environmental Research Institute, Sonoma, California, USA


Philip B. Russell

NASA Ames Research Center, Moffett Field, California, USA


Abstract

Using measurements of the spectral solar radiative flux and optical depth for 2 days (24 August and 6 September 2000) during the SAFARI 2000 intensive field experiment and a detailed radiative transfer model, we estimate the spectral single scattering albedo of the aerosol layer. The single scattering albedo is similar on the 2 days even though the optical depth for the aerosol layer was quite different. The aerosol single scattering albedo was between 0.85 and 0.90 at 350 nm, decreasing to 0.6 in the near infrared. The magnitude and decrease with wavelength of the single scattering albedo are consistent with the absorption properties of small black carbon particles. We estimate the uncertainty in the single scattering albedo due to the uncertainty in the measured fractional absorption and optical depths. The uncertainty in the single scattering albedo is significantly less on the high-optical-depth day (6 September) than on the low-optical-depth day (24 August). On the high-optical-depth day, the uncertainty in the single scattering albedo is 0.02 in the midvisible whereas on the low-optical-depth day the uncertainty is 0.08 in the midvisible. On both days, the uncertainty becomes larger in the near infrared. We compute the radiative effect of the aerosol by comparing calculations with and without the aerosol. The effect at the top of the atmosphere (TOA) is to cool the atmosphere by 13 W m−2 on 24 August and 17 W m−2 on 6 September. The effect on the downward flux at the surface is a reduction of 57 W m−2 on 24 August and 200 W m−2 on 6 September. The aerosol effect on the downward flux at the surface is in good agreement with the results reported from the Indian Ocean Experiment (INDOEX).

Published 18 February 2003.

Index Terms: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0360 Atmospheric Composition and Structure: Transmission and scattering of radiation; 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing.

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Citation: Bergstrom, R. W., P. Pilewskie, B. Schmid, and P. B. Russell (2003), Estimates of the spectral aerosol single scattering albedo and aerosol radiative effects during SAFARI 2000, J. Geophys. Res., 108(D13), 8474, doi:10.1029/2002JD002435.