SUBSURFACE, SURFACE, AND RADAR MODELING OF A GULF-STREAM CURRENT CONVERGENCE

In this paper we investigate the underlying dynamics associated with a strong, line-shaped submesoscale feature that was observed in radar i magery at the boundary between Gulf Stream (GS) and shelf water near C ape Hatteras during the first Naval Research Laboratory High-Resolutio n Remote Sensing Experiment (HIRES 1). The line-shaped feature, which appears as a pronounced (similar to 10 dB) increase in radar cross sec tion, extends several kilometers in the east-west direction. In situ c urrent measurements have shown that this feature coincides with the bo undary of a sharp current convergence front. These measurements also i ndicate that the frontal dynamics is associated with the subduction of denser GS water under lighter shelf water. Using the observation that the convergence can be attributed to a hydrodynamic instability at th e water interface, we have modeled the resulting subsurface hydrodynam ics on the basis of a rigid-lid, two-dimensional solution of the Navie r Stokes equation. The calculations of subsurface current flow were us ed as input to a spectral (wave action) model of wave-current interact ion to obtain the surface wave field, which in turn was used to provid e input for modeling of radar backscatter. The resulting description a lso includes the effects of surfactant-induced wave damping on electro magnetic backscatter. Our predictions are compared with real aperture radar imagery and in situ measurements from the HIRES 1 experiment.