INTERACTION OF SHORT SURFACE AND ELECTROMAGNETIC-WAVES WITH OCEAN FRONTS

The interaction of short surface waves with shearing and converging currents is investigated by means of an approximate analytical solution of the wave action spectral transport equation. Spectral perturbations of less than 10% are predicted at centimeter wavelengths for moderately strong ocean fronts, although much larger perturbations are expected at wavelengths of the order of 1 m. These results, when combined with a simple Bragg electromagnetic scattering model, do not explain the large backscatter variations observed at X band and C band in the vicinity of ocean fronts. A two-scale electromagnetic scattering model provides an effective coupling between the long-wave spectral perturbations and the radar backscatter at small incidence angles, but this mechanism becomes less effective at intermediate incidence angles. Observation of large backscatter variations at these angles may thus be an indication of additional hydrodynamic and/or electromagnetic scattering mechanisms that are not yet accounted for.