HF radar observations of small‐scale surface current variability in the Straits of Florida

A dual‐station high‐frequency Wellen radar (WERA), transmitting at 16.045 MHz, was deployed along the eastern Florida Shelf and operated and maintained by the University of Miami's Rosenstiel School of Marine and Atmospheric Science. From September 2004 to June 2005, a moored acoustic Doppler current profiler (ADCP) acquired subsurface current measurements within the radar footprint along the shelf break at 86‐m depth. The shallowest ADCP bin located at 14‐m depth was used as a comparison for the WERA surface measurements. RMS differences ranged from 0.1 to 0.3 m s −1 between the surface and 14‐m depth, with good agreement over most of the period. Regression analyses indicated slopes near unity in the north‐south ( v ) component and ≈0.5 for the east‐west ( u ) component velocities. When utilized in tandem with the ADCP subsurface measurements, WERA enables three‐dimensional snapshots of coastal oceanographic features to be resolved. For example, from December 2004 through February 2005, three energetic circulation patterns were observed: (1) a subsurface stratified countercurrent, (2) a submesoscale coherent vortex, and (3) a mesoscale circulation feature, i.e., a propagating Tortugas gyre. These features represent the significant current variability along the western flank of the Florida Current that impacts the coastal ocean.