Energy transfer between hydrodynamically modulated long and short ocean waves by interaction with the wind field

Radar signatures of spatially varying surface currents, such as found over underwater bottom topography in tidal waters, are often underestimated by theoretical models. After the development of advanced radar backscattering models which account for contributions of the entire ocean wave spectrum, this is usually attributed to shortcomings of existing wave-current interaction theories. In this paper we discuss results of a comprehensive analysis of radar images and in-situ wave and wind data that were acquired during the C-STAR experiment over underwater bottom topography in the North Sea. As expected, measured radar signatures and intensity variations of short waves are underestimated by a conventional model. Clear improvement is obtained after introducing a modified equilibrium wave spectrum and spatial wind stress variations as given by buoy data. Our results suggest that a surface roughness-wind stress feedback mechanism exists, which leads to a coupling between intensity variations of short ripple waves and longer waves via interaction with the wind field.