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Title: Solar and thermal radiative effects during the 2011 extreme desert dust episode over Portugal
Authors: Valenzuela, Antonio
Costa, Maria João
Guerrero-Rascado, Juan Luis
Bortoli, Daniele
Olmo, Francisco Jose
Keywords: Aerosol vertical profiles
Radiative forcing
Issue Date: Jan-2017
Publisher: Elsevier
Citation: Valenzuela, A., M.J. Costa, J.L. Guerrero-Rascado , D. Bortoli, F.J. Olmo, 2017: Solar and thermal radiative effects during the 2011 extreme desert dust episode over Portugal. Atmospheric Environment 148 (2017) 16-29. Doi: 10.1016/j.atmosenv.2016.10.037
Abstract: This paper analyses the influence of the extreme Saharan desert dust (DD) event on shortwave (SW) and longwave (LW) radiation at the EARLINET/AERONET Évora station (Southern Portugal) from 4 up to 7 April 2011. There was also some cloud occurrence in the period. In this context, it is essential to quantify the effect of cloud presence on aerosol radiative forcing. A radiative transfer model was initialized with aerosol optical properties, cloud vertical properties and meteorological atmospheric vertical profiles. The intercomparison between the instantaneous TOA shortwave and longwave fluxes derived using CERES and those calculated using SBDART, which was fed with aerosol extinction coefficients derived from the CALIPSO and lidar-PAOLI observations, varying OPAC dataset parameters, was reasonably acceptable within the standard deviations. The dust aerosol type that yields the best fit was found to be the mineral accumulation mode. Therefore, SBDART model constrained with the CERES observations can be used to reliably determine aerosol radiative forcing and heating rates. Aerosol radiative forcings and heating rates were derived in the SW (ARFSw, AHRSw) and LW (ARFLw, AHRLw) spectral ranges, considering a cloud-aerosol free reference atmosphere. We found that AOD at 440 nm increased by a factor of 5 on 6 April with respect to the lower dust load on 4 April. It was responsible by a strong cooling radiative effect pointed out by the ARFSw value (−99 W/m2 for a solar zenith angle of 60°) offset by a warming radiative effect according to ARFLw value (+21.9 W/m2) at the surface. Overall, about 24% and 12% of the dust solar radiative cooling effect is compensated by its longwave warming effect at the surface and at the top of the atmosphere, respectively. Hence, larger aerosol loads could enhance the response between the absorption and re-emission processes increasing the ARFLw with respect to those associated with moderate and low aerosol loads. The unprecedented results derived from this work complement the findings in other regions on the modifications of radiative energy budget by the dust aerosols, which could have relevant influences on the regional climate and will be topics for future investigations.
Type: article
Appears in Collections:ICT - Publicações - Artigos em Revistas Internacionais Com Arbitragem Científica
FIS - Publicações - Artigos em Revistas Internacionais Com Arbitragem Científica
CGE - Publicações - Artigos em Revistas Internacionais Com Arbitragem Científica

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