NUMERICAL-SIMULATION OF THE DYNAMICS OF SEA SPRAY OVER THE WAVES

SeaCluse is a code describing and quantifying the nonlinear interactio ns between spray droplet concentrations and the scalar fields of water vapor concentration and temperature in the marine atmospheric surface layer as a function of the basic micrometeorological parameters. It i s currently developed to simulate most of the dynamics of the evaporat ing sea spray droplets, their transformations, and their influence on the structure of the marine lower atmosphere. It includes two parts, a ''preprocessor'' computing the air flow structure and droplet traject ories over the waves in the absence of turbulence and evaporation, and a ''main program'' computing along the vertical the horizontally aver aged budgets of droplet and water vapor concentrations, and sensible h eat, including the dynamic and thermodynamic air-droplet interactions. This paper presents the first simulations, without evaporation, which reveal several characteristic features of the spray droplet dynamics over the waves. The mean air flow induced by the wave motion generates an efficient transport of many droplets up to the wave crest level or Slightly higher, where they accumulate. In contrast, turbulence appea rs to be a rather inefficient process to elevate further the droplets that have nonnegligible weight and inertia (and an efficient process f or very small droplets). The residence times in the air T-fly of dropl ets larger than 90 mu in radius do not increase much, compared to thei r values in still air or over a flat surface, and they increase with i ncreasing wind speed much less rapidly than the wave height H-o: T-fly similar to U-0.3 while H-o similar to U-2. Above the wave crest, the droplet concentrations are several orders of magnitude smaller than be tween wave troughs and crests. The precision of the turbulent diffusiv ity model for droplets therefore appears crucial to correctly infer th e spray surface source function from concentration measurements id the atmosphere.