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. This raises the issue of whether functions such as the turbulent kinetic energy (TKE) budget and Monin-Obukhov similarity theory (MOST) determined over land are directly applicable to ocean surfaces 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, and wave coherent stress accounts for the momentum transfer between ocean waves and atmosphere. In this study, applications of the turbulent kinetic energy (TKE) budget and the inertial dissipation method (IDM) in the context of the Monin-Obukhov similarity theory (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 combing the TKE budget and MOST, our study showed that the stress computed by the traditional IDM corresponds to turbulent stress rather than total stress. The swell wave coherent stress should be considered when applying the IDM to calculate the stress in the WBL.