Sea spray transport modeling in the North-West Mediterranean with a coupled wave-atmosphere numerical model combining the MESO-NH atmospheric model and the ECMWF HRES-WAM wave model, using a new sea spray production source function determined from both tunnel and field observations.

Research conducted over the past four decades has shown that sea spray production and transport plays an important role in heat and humidity transfers in the marine atmospheric boundary layer (MABL), thus affecting the global climate. Implementing a sea spray source function (S3F) in current numerical weather prediction is therefore of great interest for the reduction of numerical weather prediction errors, especially in extreme wind speed conditions in which sea spray is thought to dominate the flux problem. To this end, a S3F model determined from a combination of tunnel and field measurements (Bruch et al., 2020) is introduced in a coupled Wave-Atmosphere numerical model using the MESO-NH atmospheric model, and the ECMWF HRES-WAM wave model. The new S3F is valid over the 3-35 μm radius and for U10 wind speeds ranging from 12 to 20 m s-1. The S3F is dependent on the sea surface characterisitics such as wave slope variance; a non-dimensional surface parameter allowing the integration of wave-wind boundary processes such as wave breaking and surface tearing that are essential for film and spume droplet production, respectively. Using this S3F, the modeled sea spray production and transport is compared with sea-spray number concentrations measured on board the Atalante research vessel during the MIRAMER campaign which took place in the Northern Mediterranean in 2008 (see Laussac et al., 2018). The surface wave slope variance representative of the field conditions is calculated using formulae existing in the literature, such as the celebrated wind-dependent semi-empirical function proposed by Cox and Munk (1956).

References: - Bruch W, Piazzola J, Branger H, Lunean C, Bourras D, van Eijk A, Tedeschi G, (2020) Sea Spray Production Dependence on Wind and Wave Combinations : A Tunnel Study. Submitted in Boundary Layer Meteorology. - Cox C, Munk W (1956) Slopes of the sea surface deduced from photographs of sun glitter. Bulletin of the Scripps Institution of Oceanography, Volume 6, Issue 9, pages 401-488. - Laussac S, Piazzola J, Tedeschi G, Yohia C, Canepa E, Rizza U, van Eijk A (2018) Development of a fetch dependent sea-spray source function using aerosol concentration measurements in the north-western Mediterranean. Atmospheric Environment 193:177-189.