Direct SW aerosol radiative forcing over Portugal

[摘要] In this work, the evaluation of the aerosol radiative forcing at the top ofthe atmosphere as well as at the surface over the south of Portugal is made,particularly in the regions of Évora (38°34' N, 7°54' W) and ofCabo da Roca (38°46' N, 9°38' W), during years 2004 and 2005.

The radiative transfer calculations, using the radiative transfer codeSecond Simulation of the Satellite Signal in the Solar Spectrum (6S),combine ground-based measurements, from Aerosol Robotic NETwork (AERONET),and satellite measurements, from MODerate Imaging Spectroradiometer (MODIS),to estimate the direct SW aerosol radiative forcing. The method developed toretrieve the surface spectral reflectance is also presented, based onground-based measurements (AERONET) of the aerosol optical propertiescombined with the satellite-measured radiances (MODIS).

The instantaneous direct SW aerosol radiative forcing values obtained at thetop of the atmosphere are, in the majority of the cases, negative,indicating a tendency for cooling the Earth at the top of the atmosphere.For Desert Dust aerosols, over the Évora land region, the averageforcing efficiency is estimated to be −25 Wm⁻²/AOT_0.55 whereas forthe Cabo da Roca area, the average forcing efficiency is −46 Wm⁻²/AOT_0.55.In the presence of Forest Fire aerosols, both fromshort and long distances, the average value of forcing efficiency at the topof the atmosphere over Cabo da Roca is found to be −28 Wm⁻²/AOT_0.55 and, over Évora,−27 Wm⁻²/AOT_0.55. Forspecific situations, discussed in this work, the average surface direct SWaerosol radiative forcing efficiency due to the Desert Dust aerosols, inÉvora region, is −66 Wm⁻²/AOT_0.55, whereas in Cabo da Rocaregion, the corresponding average value is −38 Wm⁻²/AOT_0.55. Considering the Forest Fire aerosols,over Évora region, the average surface directSW aerosol radiative forcing efficiency can vary between −36 and −113 Wm⁻²/AOT_0.55, themore negative value corresponding to forest fire aerosols coming only from shorter distances.

[学科分类] 大气科学