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 (AT T ) and aerosol optical depth (AOD T ) 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 (AOD S ) and albedo over a region of the North Atlantic Ocean extending from 15°–35°N to 12°–25°W. We observe large changes in AT T and AOD T 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 AOD T and we compute the direct radiative forcing Δ F attributable to mineral dust. The local radiative forcing obtained is over the ocean Δ F = −9.7 W/m 2 and for the land Δ F = −4.5 W/m 2 with an error of ±25%. Extending these results to global‐scale averages, we obtain values of Δ F of −1.22 W/m 2 over the ocean and −0.57 W/m 2 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.