Wind Stress from Wave Slopes Using Phillips Equilibrium Theory

Abstract

An open ocean, deep water air–sea interaction experiment was conducted in the Gulf of Alaska. Wave amplitude and slope data were measured using a WAVEC heave, pitch, and roll buoy that was let drift in the Alaska gyre. Wind stress estimates were obtained from a fast-sample anemometer using the dissipation technique and from synoptic measurements through a boundary-layer model. The fundamental correlation and predictive relationships between wind friction velocity and wave spectral properties were established. A comparison of the slope spectrum to simultaneous wind stresses allowed us to estimate the Phillips proposed universal constant β. Reintroducing this constant β into the Phillips slope spectrum and using measured slope spectral characteristics, an inferred wind stress was calculated that was shown to agree well with both the dissipation and model stresses thereby validating both Phillips theory and the boundary-layer model. Any discrepancies with the model stresses were attributed to second-order wave age effects. The roughness length z0, nondimensionalized by the sea rms wave height, was shown to decrease with wave age in a manner consistent with Kitaigorodskii's functional form. A general expression for Cd as a function of wind speed or friction velocity and wave age was proposed and verified with independent data.