Identifying the shoreward Gulf Stream front at Cape Hatteras with Coastal Ocean Radar surface currents

Surface currents off of Cape Hatteras North Carolina observed with a 5 MHz coastal ocean radar were analyzed to determine the location and variability of the shoreward edge of the Gulf Stream based on the region of maximum horizontal shear. The method for identifying the front is described in detail. A Coastal Ocean Radar (Codar) from Codar Ocean Sensors installed on the beach in Buxton, North Carolina has been operating from the fall of 2003 until the present. The Codar measures the radial component of the surface current and has a range from 100 to 200 km with spatial resolution decreasing as a function of range in 5.85 km range cell increments. Each radial vector produced is an average in an annulus bounded by a 5.85 km range difference and a five-degree bearing difference. The most probable location for the shoreward location of the Gulf Stream front is identified by the maximum horizontal shear in the radial velocities. Frontal locations are estimated by the maximum derivative of the radial speed with respect to bearing at a given range, and by the maximum derivative with respect to range at a given bearing. A third order piecewise spline curve was then fit to the combined set of gradient components. The locations where the Gulf Stream first enters and exits the radar coverage area are apparent in the large radial speeds measured by the radar, however in a region between these two zones the Gulf Stream is perpendicular to the radar, and the radar can not provide a good approximation for stream location based on this method.