Vertically Resolved Direct Radiative Effects of Intense Mediterranean Dust Episodes during the Period 2005–2018

Abstract

In the present study, the all-sky Dust Direct Radiative Effect (DDRE) is estimated during intense Dust Aerosol (DA) episodes that took place from 2005 to 2018 over the broader Mediterranean Basin (MB). DA episodes are identified using a satellite algorithm, which is based on aerosol optical properties. The DDREs are estimated using a vertically resolved version of the FORTH spectral radiative transfer model (RTM). The RTM ran on a 3-hourly temporal and 0.5° × 0.625° horizontal spatial resolution for each of the 162 identified DA episode days (DAEDs), initialized with 3D dust and total (all) aerosol optical properties, namely optical depth, single scattering albedo, and asymmetry parameter from the MERRA-2 reanalysis. Cloud data (cloud amount, optical depth, and top pressure) are taken from the ISCCP-H. The RTM computes the upwelling and downwelling solar fluxes at TOA, at the surface, and at 50 levels in the atmosphere. The runs were made with all aerosols, and all but DA. The DDREs were calculated by the difference between the two sets of output fluxes. According to the model results averaged over the 162 studied episodes, DA reduces the net surface solar radiation over the MB, causing a cooling effect as large as −77 W/m2 (climatological mean value at 12:00 UTC) over areas with high dust optical depth. On the contrary, they increase the atmospheric absorbed solar radiation, resulting in considerable (up to 79 W/m2) atmospheric radiative heating. At TOA, either heating (up to 30 W/m2 over desert areas) or cooling (as strong as −21 W/m2 over oceanic areas) are found, depending on the significantly different underlying surface albedos. DDREs are even higher during single episodes, with a surface cooling effect as large as −200 W/m2 and a corresponding atmospheric heating effect of up to +187 W/m2.

Keywords

• aerosols
• dust episodes
• direct radiative effect
• Mediterranean