Atmospheric Boundary Layer Turbulence in the Presence of Swell: Turbulent Kinetic Energy Budget, Monin-Obukhov Similarity Theory, and Inertial Dissipation Method

Turbulence over the mobile ocean surface has distinct properties compared to turbulence over land. Thus, findings that are based on the turbulent kinetic energy (TKE) budget and Monin-Obukhov similarity theory (MOST) over land may not be applicable to conditions over ocean partly because of the existence of a wave boundary layer (the lower part of atmospheric boundary layer including effects of surface waves; we used the term WBL in this article for convenience), where the total stress can be separated into turbulent stress and wave coherent stress. Here the turbulent stress is defined as the stress generated by wind shear and buoyancy, while the wave coherent stress accounts for the momentum transfer between ocean waves and atmosphere. In this study, applicability of the turbulent kinetic energy (TKE) budget and the inertial dissipation method (IDM) in the context of the MOST within the WBL are examined. It was found that turbulent transport terms in the TKE budget should not be neglected when calculating the total stress under swell conditions. This was confirmed by observations made on a fixed platform. The results also suggested that turbulent stress, rather than total stress, should be used when applying the MOST within the WBL. By combining the TKE budget and MOST, our study showed that the stress computed by the traditional IDM corresponds to the turbulent stress rather than the total stress. The swell wave coherent stress should be considered when applying the IDM to calculate the stress in the WBL.