We present results of direct aerosol radiative forcing over a French Mediterranean coastal zone based on one year of continuous observations of aerosol optical properties during 2005-2006. Monthly-mean aerosol optical depth at 440 nm ranged between 0.1 and 0.34, with high Angstrom coefficient (α N 1.2). The single scattering albedo (at 525 nm) estimated at the surface ranged between 0.7 and 0.8, indicating significant absorption. The presence of aerosols over the Mediterranean zone during summer decreases the shortwave radiation reaching the surface by as much as 26 ± 3.9 W m − 2 , and increases the top of the atmosphere reflected radiation by as much as 5.2 ± 1.0 W m − 2 . The shortwave atmospheric absorption translates to an atmospheric heating of 2.5 to 4.6 K day − 1 . Concerted efforts are needed for investigating the possible impact of the increase in heating rate on the maintenance of heat-waves frequently occurring over this coastal region during summer time.

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Abstract. The performance of electro-optical systems can be substantially affected by aerosol particles that scatter and absorb electromagnetic radiation. The model that is most frequently used for the prediction of aerosols and their effect on extinction in the marine atmosphere is the US Navy Aerosol Model (NAM). However, NAM can be significantly less reliable in coastal areas than on the open ocean. Based on an extensive series of measurements conducted on the island of Inisheer (Irish West Coast), an empirical aerosol model for the coastal zone formulated as an extension of NAM, in which coastal effects are modeled as a function of fetch, has been developed. This work is extended to the Mediterranean using an aerosol dataset recorded on the island of Porquerolles in the Bay of Toulon (France) and has been coupled with the Mie theory to give a code for the extinction, the code MEDiterranean EXtinction (MEDEX).