Studying the effect of sea spray using large eddy simulations coupled with air–sea bulk flux models under strong wind conditions

Abstract

Three high resolution large eddy simulations (LES) with two bulk air–sea flux algorithms, including the effects of water phase transition, are performed in order to study the influence of sea spray on the marine atmospheric boundary layer (MABL) structure and cloud properties. Because sea spray has a notable impact under severe wind conditions, the CBLAST-Hurricane experiment supplies the initial realistic conditions as well as turbulence measurements for their assessment. However a hurricane boundary layer (HBL) simulation is not in the scope of this study. Although the simulations in the final state depart from the initial conditions, all three momentum flux distributions are found at the low end of the observed range. The spray-mediated sensible heat flux is opposite to the interfacial flux and reaches up to 60% of its magnitude. When the spray-mediated contribution is taken into consideration, the simulated moisture flux increases by up to 45% and gets closer to the observations. Small scale stream-wise velocity streaks are arranged, probably due to spray effects, into large scale structures where the scalars' variations tend to concentrate. However, the vertical velocity structure below mid-MABL is not greatly affected as the buoyancy forces locally within these structures are negligible. Spray effects greatly enhance the magnitude of the quadrant components of the scalar fluxes, but the net effect is less pronounced. Spray-mediated contribution results in more extended cloud decks in the form of marine stratocumulus with increased liquid water content. The visually thicker clouds reduce the total surface radiation by up to 30 \({\text{Wm}}^{-2}\).