The coherence of wind and radar data obtained during the Joint US-Russia Internal Wave Experiment

The rate at which short surface waves relax to equilibrium after a perturbation is a key parameter in models of the modulation of surface waves by internal waves. The authors report on an investigation of the short wave relaxation rates by statistical comparisons of fluctuations in the near surface wind speed under unstable conditions and variations in the backscatter cross section from an airborne radar. Data for this study were obtained during the Joint US/Russia Internal Wave Remote Sensing Experiment. During this experiment wind speed was measured from both a ship and a buoy. Ku-band, vertically-polarized radar data were obtained for a range of look directions. The estimation of short-wave growth and dissipation rates are discussed. The authors show that if the dissipation term appearing on the right hand side of the wave action balance equation is written in terms of a power law in wave energy, Eⁿ, and the nonlinear energy transfer is small, then the exponent, n, is related to the wind dependence of the radar backscatter. This analysis suggests that scatterometer data obtained at different angles relative to the wind direction could prove useful in the development of new spectral relaxation models.