Flux-Profile Relations over Water Surfaces: Disentangling the Influences of Stability and Waves

Air-wave interactions over water surfaces significantly influence momentum and scalar transport, and parameterizations of surface fluxes that are developed for land might not be directly applicable. In this study, we analyzed surface wave measurements and eddy covariance data collected during the Lake-Atmosphere Turbulent EXchange (LATEX) field measurement campaign over lake Geneva to explore the exchanges at the water-air interface. The findings indicate that the momentum transport efficiency is dependent on the angle α between the mean wind direction and the wave propagation direction. The appropriate velocity scale is then shown to also depend on α. This new insight enables us to propose a modified form of the Monin-Obukhov similarity theory (MOST) over waves that is shown to be a better fit for the measured data. α mainly affects the pressure drag, and therefore the momentum exchange, while the scalar efficiency is found to be insensitive wind-wave misalignment. The scalar to momentum roughness lengths ratio (z0m/zos)), computed using the new form of MOST, is found to follow previously proposed models reasonably well, and to depend on wave steepness.