| Using a very high frequency surface current radar deployed along the South Florida coast during July 1999 and April 2000, 2001, surface velocity measurements have revealed intrusions of a western boundary current across the shelf break and wind-driven flows. Over a 6 km x 8 km domain, the radar mapped the evolving current at 700 cells with a horizontal resolution of 250 m at 20-min intervals. In addition to the surface currents associated with the Florida Current, energetic, cyclonically rotating vortices translated through the domain at speeds of 30 cm s-1 with diameters of a few kilometers. Along the inshore edge of the Florida Current, the normalized vorticity ranged between 2 to as high as 5f, where f is the local Coriolis parameter. Subsurface current comparisons to acoustic Doppler current profiler measurements indicate RMS differences of 10 to 20 cm s-1 from moorings and autonomous underwater vehicles (AUV) in this energetic domain. Concurrent wind measurements were acquired at Coastal Marine Autonomous Network stations and at surface moorings within the radar domain. Under light winds in July 1999, spatially averaged current profiles from several current snapshots from an AUV were time-averaged to form mean profiles. In the down-wind directions, these mean profiles were compared to a wind-driven log layer profile in the upper 6.5 m based on a 10-m surface winds. Regression analyses suggest a slope of ~ 1.16 between the theoretical and observed mean current profiles with a bias of about 3 cm s-1. A more energetic surface current response was observed during the passage of an atmospheric front in April 2000. Since the Florida Current was well offshore during this period, analyses revealed that surface currents ranged between 35 to 45 cm s-1. During frontal passage, the corresponding surface winds from an Air-Sea Interaction Spar buoy ranged between 10 to 14 m s-1. Observed surface current of 35 to 50 cm s-1 scaled well with theoretical estimates based on ~3.6% of the surface winds. Moreover, the spatial response of the surface velocity field moved at speeds of about 2 km h-1, and was well correlated with the passage of the atmospheric front. |
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