Spatial variation of the aerosol concentration over a Mediterranean coastal zone and implication on the infrared extinction

Abstract

The performance of electro-optical systems can be substantially affected by aerosol particles that scatter and absorb electromagnetic radiation. While molecular extinction can be calculated using propagation codes such as MODTRAN (Berk et al., 1989), the influence of aerosols is much less easy to account for. However, concentrations and optical properties of aerosol particles in the atmosphere are quite variable both in time and space. Very few relevant models for the aerosol size distributions have been published during the last decades. One of the most used is the Navy aerosol model (NAM, Gathman, 1983), which is currently being upgraded to the advanced Navy aerosol model (ANAM, van Eijk and Merritt, 2006). NAM and ANAM are dedicated to open ocean, while coastal areas induce specific processes (Piazzola et al., 2000, and Bendersky et al., 2004). To include coastal effects for the prediction of aerosol concentrations and their effects on the extinction, Piazzola et al. (2003) proposed the aerosol extinction code MEDEX. We deal with the extension of the predictions of MEDEX on a regional scale. To achieve it, MEDEX is forced by the regional mesoscale meteorological model RAMS (Cotton et al., 2003) to account for the fine details of the coastal orography. Simulations are then compared to aerosol size distributions recorded in the Mediterranean. The results show a nonhomogeneous spatial coverage of the aerosol concentrations over the northern Mediterranean. In addition, we show the least performance of the coupling for unsteady conditions of the wave field.