Issues surrounding surfactant effects upon radar imagery of convergent ocean surface flows with application to the Hi-Res I rip feature

X-band radar signatures of a current rip convergence, resulting from denser Gulf Stream fluid interacting with fresh coastal shelf water near Cape Hatteras, were observed during the First High Resolution (Hi-Res I) experiment. These signatures, which appeared as intense (/spl sim/10 dB) enhancements in radar cross section (RCS) in the form of meandering linear segments, were accompanied by secondary parallel meandering segments of reduced (/spl sim/5-10 dB) RCS on the shelf water side. The effects of wave-current interaction scale with the surface velocity (u) while the effects of surfactants scale as the ratio of surface current to phase velocity (u/c). Unlike internal waves which 'graze' upon the ambient surface film material, current rips 'herd' the ambient surface film material to a convergence point where u/c=1. The latter features can induce singular behaviour for a monomolecular surface film. A number of fundamental issues need to be resolved including: continuity of the surface film in regions of wave breaking; buckling of the monomolecular film; and subduction of the surfactant at the frontal boundary. These issues are highlighted through application to the Hi-Res I rip feature using a simplified one-dimensional model of the feature as well as the surface manifestation of currents derived from the associated depth-dependent structure.