Buzzards Bay Air-Sea Interaction Tower (BB-ASIT) water column data from Fall 2022 deployment

Abstract

Data from an air-sea interaction tower are used to close the turbulent kinetic energy (TKE) budget in the wave-affected surface layer of the upper ocean. Under energetic wind forcing with active wave breaking, the dominant balance is between the dissipation rate of TKE and the downward convergence in vertical energy flux. The net energy flux is downward, primarily driven by pressure work, and the TKE transport is upward, opposite to the downgradient assumption in most turbulence closure models. The sign and the relative magnitude of these energy fluxes are hypothesized to be driven by a weak interaction between the vertical velocity of Langmuir circulation (LC) and the kinetic energy and pressure of wave groups that is the result of small scale wave-current interaction. Consistent with previous modeling studies, the data suggest that the horizontal current anomaly associated with LC refracts wave energy away from downwelling regions and into upwelling regions, resulting in negative covariance between the vertical velocity of LC and the pressure anomaly associated with the wave groups. The asymmetry between downward pressure work and upward TKE flux is explained by the Bernoulli response of the sea-surface, which results in groups of waves having a larger pressure anomaly than the corresponding kinetic energy anomaly, consistent with group-bound long wave theory.