The interaction of Ocean Surface Processes, Waves, and Turbulence in the Adjacent Boundary Layers

In order for air–sea exchange processes to be estimated in a dynamically consistent manner in the coupled atmosphere–ocean boundary-layer system, it is necessary to account for the dynamics of surface waves and other movements of the air–water interface. This is also necessary for the interpretation of turbulent flux observations made within the boundary layers, particularly those made from non-stationary measurement platforms. In recent years, considerable progress has been made in observational technology for the direct determination of the vertical flux of momentum, heat, and mass by eddy covariance techniques. We present an approach to the study of atmosphere–ocean boundary-layer fluxes which employs a general time-dependent coordinate formulation. To provide a uniform treatment both above and below the water surface it is advantageous to use the instantaneous sea surface as a coordinate surface. Reynolds covariances for turbulent flux are then replaced by more complex expressions, and we explore the implications for the design of flux measurement systems and modelling of the coupled interfacial/boundary-layer system. We show that for the flux of trace substances, and other scalar quantities such as heat, measurements of averaged fluxes from moving measurement platforms are subject to biases which are proportional to the square of the amplitude of the platform displacement or of the wave slope, and we indicate how such biases may be corrected or allowed for.