Results of X-band microwave backscatter from sea surfaces at a small-grazing angle for a range of wind speeds (3.8-10.3 d s ) are presented. The data indicate that the speed of faster-than-Bragg scatterers and their time-averaged polarization ratio both increase with wind speed. At a friction velocity above -21 c d s , super events (i.e., backscattering events where the horizontal-polarization power exceeds the vertical-polarization power) begin to appear. The fraction of fast scatterers which produce super events also increases with wind speed. The presence of super events indicates that in addition to scattering mechanisms, such as Bragg-resonant scattering, composite surface theory, wedge scattering, and specular reflection, other mechanisms which favor the horizontal-polarization returns must be considered.

Langmuir circulations in a wind wave tank have been observed and measured by a variety of methods including dye patterns and floating surface tracers. On the basis of measurements of cellular wavelength λc as a function of surface wavelength λw and depth H a tentative functional relation for the dependence of λc/H upon λw/H is proposed. The experiments clearly imply that the waves play an important role in the mechanism of formation of the Langmuir circulations but that the depth of the layer has a significant modifying influence. On the basis of certain ‘rake’ experiments and other indirect observations it is proposed that when λw/H < 1, the primary scale of Langmuir circulations, related to λw, transfers energy to a larger scale that is commensurate with the depth such that λc/H ≃ 2. Under these circumstances, two distinct scales of Langmuir circulations may exist simultaneously.

Calculations of surface wave and radar cross section modulation induced by a spatially varying surface current have been compared with field measurements made with synthetic aperture radar (X and L bands), real aperture radar ( X band), laser slope gauge, and charge‐coupled device video camera during the Joint Canada‐U.S. Ocean Wave Investigation Project (JOWIP), which took place in August 1983. The comparison reveals that (1) many existing wind relaxation models underpredict the hydrodynamic effect of the current, (2) the simple Bragg scattering model underpredicts radar backscatter modulation for higher‐frequency radars (e.g., X band) but appears acceptable at lower radar frequencies (e.g., L band), and (3) the discrepancy between measurements and calculations at high radar frequency is reduced, but not eliminated, when the effects of long surface waves have been accounted for.

The steady, laminar, incompressible flow over a periodic wavy surface with a prescribed surface-velocity distribution is found from the solution (via Newton's method) of the two-dimensional Navier–Stokes equations. Validation runs have shown excellent agreement with known analytical (Benjamin 1959) and analytico-numerical (Bordner 1978) solutions for small-amplitude wavy surfaces: For steeper waves, significant changes are observed in the computed surface-pressure distribution (and consequently in the nature of the momentum flux across the interface) when a surface orbital velocity distribution, of the type found in water waves, is included,

A simple water-wave instability induced by a shear flow is reexamined , using a cubic equation first derived by Stern & Adam (1973) for a piecewise constant vorticity model. The instability criteria and the growth rate are computed. It is found that this mechanism is effective only if the surface drift velocity exceeds the minimum wave speed for capillary-gravity waves, and only if the drift-layer thickness lies within a band which depends on the wavelength and the drift velocity.