Radiative properties of aerosols in Saharan dust outbreaks using ground-based and satellite data: Applications to radiative forcing

Abstract

We report on measurements of atmospheric transmission (ATτ) and aerosol optical depth (AODτ) made at three wavelengths (368, 500, and 778 nm) with a spectroradiometer placed on Tenerife (28.5° N, 16.3° W), Canary Islands. Using the National Oceanic and Atmospheric Administration (NOAA) advanced very high resolution radiometer (AVHRR) channel 1, we also measured the aerosol optical depth (AODs) and albedo over a region of the North Atlantic Ocean extending from 15°-35° N to 12°-25° W. We observe large changes in ATτ and AODτ when dust outbreaks pass over this region. Using all these data, we derive the asymmetry factor (g), the single-scattering albedo (ω), and the local mean AODτ and we compute the direct radiative forcing ΔF attributable to mineral dust. The local radiative forcing obtained is over the ocean ΔF=-9.7 W/m2 and for the land ΔF=-4.5 W/m2 with an error of ±25%. Extending these results to global-scale averages, we obtain values of ΔF of -1.22 W/m2 over the ocean and -0.57 W/m2 over land. The forcings attributable to dust are comparable in magnitude to those reported in the literature for anthropogenic sulphate and for biomass burning aerosols. Copyright 2001 by the American Geophysical Union.