Detection and interpretation of ocean roughness variations across the gulf stream inferred from radar cross section observations

During the past several years, many radars have observed the distinct and interesting features associated with the Gulf Stream and its boundaries. Some of these Gulf Stream radar features have small scale, with dimensions comparable to and slightly greater than long gravity waves. Other features are larger, with dimensions much greater than the length of long gravity waves. This study describes radar cross section variations within the Gulf Stream and just outside, seen with a "scatterometer" type measurement. The significant features of this radar cross section data were that the Gulf Stream always had a higher cross section per unit area (interpreted here as a greater roughness) than the water on the continental shelf. Also, a steep gradient in cross section was often seen at the expected location of the western boundary. There were also longer scale (10 to 20 km) gradual fluctuations within the stream of significant magnitude. These roughness variations are correlated with the surface shear stress that the local wind imposes on the sea. Using the available surface truth information regarding the wind speed and direction, an assumed Gulf Stream velocity profile, and high resolution ocean surface temperature data obtained by the Very High Resolution Radiometer onboard a NOAA-NESS polar-orbiting satellite (data provided by Dr. Richard Legeckis of NOAA-NESS), this study demonstrates that the computed surface stress variation bears a striking resemblence to the measured radar cross-section variations.