A numerical coupled model for studying air–sea–wave interaction

Abstract

A numerical coupled model of air–sea–wave interaction is developed to study the influence of ocean wind waves on dynamical, turbulent structures of the air–sea system and their impact on coupled modeling. The model equations for both atmospheric and oceanic boundary layers include equations for: (1) momentum, (2) a k-ε turbulence scheme, and (3) stratification in the atmospheric and oceanic boundary layers. The model equations are written in the same form for both the atmosphere and ocean. In this model, wind waves are considered as another source of turbulent energy in the upper layer of the ocean besides turbulent energy from shear production. The dissipation ε at the ocean surface is written as a linear combination of terms representing dissipation from mean flow and breaking waves. The ε from breaking waves is estimated by using similarity theory and observed data. It is written in terms of wave parameters such as wave phase speed, height, and length, which are then expressed in terms of friction velocity. Numerical experiments are designed for various geostrophic winds, wave heights, and wave ages, to study the influence of waves on the air–sea system. The numerical simulations show that the vertical profiles of ε in the atmospheric and oceanic boundary layers (AOBL) are similar. The magnitudes of ε in the oceanic surface zone are much larger than those in the atmospheric surface zone and in the interior of the oceanic boundary layer (OBL). The model predicts ε distributions with a surface zone of large dissipation which was not expected from similarity scaling based on observed wind stress and surface buoyancy. The simulations also show that waves have a strong influence on eddy viscosity coefficients (EVC) and momentum fluxes, and have a dominated effect on the component of fluxes in the direction of the wind. The depth of large changes in flux magnitudes and EVC in the ocean can reach to 10–20 m. The simulations of surface drift currents confirm that the currents are overestimated if the surface waves are not considered.