Cloud effects on the solar and thermal radiation budgets of the Mediterranean basin

• This paper estimates the cloud effects on the shortwave, longwave and all-wave radiation budget of the Mediterranean basin.
• The shortwave cloud effect exceeds the longwave one at both surface and top of the atmosphere, thus producing a cooling.
• Low-level clouds play a primary role for all-wave radiation at the top of atmosphere while high clouds at surface.

The cloud effects on the shortwave (SW), longwave (LW) and net all-wave radiation budgets of the Mediterranean basin were computed using a detailed radiative transfer model together with satellite and reanalysis data for surface and atmospheric properties. The model radiation fluxes at TOA were validated against CERES and ERBE satellite data, while at the Earth's surface they were validated against ground-based GEBA and BSRN station measurements. The cloud radiative effects were obtained for low, middle, high-level clouds, and for total cloud cover. Overall for the basin, the effect on solar radiation is to produce radiative cooling at the top of atmosphere (TOA) and at the surface that more than balances the warming effects on terrestrial radiation. The result is a net radiative cooling at TOA and at the surface, equal to − 18.8 and − 15.9 Wm− 2, respectively. The low-level clouds are most important for the TOA budget through significant SW reflection and little LW emission to space. High clouds play an important role in net surface cooling (− 9.8 Wm− 2) through the combination of SW reflection to space and a much reduced LW warming effect at the surface. The geographical patterns of the effects are mainly characterized by a strong south to north increasing gradient. The seasonal variation of net radiative effects is dominated by solar radiation with maxima in spring and minima in winter.