Spectral surface albedo over Morocco and its impact on radiative forcing of Saharan dust

Abstract

This journal is published under the terms of the Creative Commons Attribution-Noncommercial 3.0 Unported LicenseIn May-June 2006, airborne and ground-based solar (0.3-2.2 mu m) and thermal infrared (4-42 mu m) radiation measurements have been performed in Morocco within the Saharan Mineral Dust Experiment (SAMUM). Upwelling and downwelling solar irradiances have been measured using the Spectral Modular Airborne Radiation Measurement System (SMART)-Albedometer. With these data, the areal spectral surface albedo for typical surface types in southeastern Morocco was derived from airborne measurements for the first time. The results are compared to the surface albedo retrieved from collocated satellite measurements, and partly considerable deviations are observed. Using measured surface and atmospheric properties, the spectral and broad-band dust radiative forcing at top-of-atmosphere (TOA) and at the surface has been estimated. The impact of the surface albedo on the solar radiative forcing of Saharan dust is quantified. In the SAMUM case of 19 May 2006, TOA solar radiative forcing varies by 12 W m(-2) per 0.1 surface-albedo change. For the thermal infrared component, values of up to +22 W m(-2) were derived. The net (solar plus thermal infrared) TOA radiative forcing varies between -19 and +24 W m(-2) for a broad-band solar surface albedo of 0.0 and 0.32, respectively. Over the bright surface of southeastern Morocco, the Saharan dust always has a net warming effect

Impact of dust aerosols on the radiative budget, surface heat fluxes, heating rate profiles and convective activity over West Africa during March 2006

“…Such studies (Tegen and Lancis, 1996;Myhre and Stordahl, 2001;Lelieveld et al, 2002;Huebert et al, 2003;Tanré et al, 2003;Abel et al, 2005;Ramanathan et al, 2007;Haywood et al, 2008;Heinold et al, 2009;Bierwirth et al, 2009;Otto et al, 2009) underline that fine aerosols (urban/industrial and/or smoke particles) decrease significantly surface incoming shortwave radiations and generally increase (or rarely decrease in some specific cases; Haywood and Shine, 1995) outgoing shortwave fluxes reflected back to space. Except in cases of pure scattering particles, the net effect for the atmosphere is positive revealing a gain of solar energy within the aerosol layer.…”

Influence of spatial heterogeneity of local surface albedo on the area-averaged surface albedo retrieved from airborne irradiance measurements

“…Bowker et al, 1985;Feister and Grewe, 1995;Aoki et al, 2002;Wuttke and Seckmeyer, 2006) deliver the local surface albedo data for point locations only, whereas satellite measurements cover larger areas (Schaaf et al, 2002). On an intermediate scale, airborne radiation measurements deliver the retrieved area-averaged surface albedo ρ ret (Webb et al, 2004;Wendisch et al, 2004;Coddington et al, 2008;Bierwirth et al, 2009).…”

A tandem approach for collocated measurements of microphysical and radiative cirrus properties

“…For each radiation component (upward/downward irradiance), SMART combines two Zeiss spectrometers, each connected by fibre wires to an optical inlet mounted on the top or at the bottom of AIRTOSS and the Learjet. The spectral range of SMART is between 300 and 2200 nm with a resolution of 3 nm for wavelengths below 1000 nm and 9-16 nm above (Wendisch et al, 2001;Bierwirth et al, 2009). The upward-looking irradiance sensor on the Learjet was placed on a stabilized platform to keep it horizontally aligned during the flights.…”