Surface current observations from a combined CODAR/WERA high-frequency radar array along the North Carolina coast during the Processes Driving Exchange at Cape Hatteras (PEACH) Project

Between April 2017 and November 2018 four medium-range WERA high-frequency radar (HFR) were deployed along the North Carolina coast, augmenting an existing array of long-range CODAR HFRs, as part of the NSF-funded Processes driving Exchange At Cape Hatteras (PEACH) project. These installations together yielded estimates of surface currents over the continental shelf around Cape Hatteras as well as the adjacent open ocean waters, including estimates of currents in the Gulf Stream and southern Slope Sea. We report on the procedure used to form vector surface current observations from all of the HFRs, the challenges posed by this procedure, the mean field observed, and a comparison of the HFR-derived velocities with independent observations. Because of the coastline geometry and the irregular spacing of HFR sites, averaging of the WERA observations was required to avoid severely biasing velocity estimates in the Gulf Stream directly offshore of Cape Hatteras. The mean velocity field captures the separation of the Gulf Stream from the upper slope, as well as the converging shelf currents and export of shelf waters to the open ocean. Based on independent observations of the currents with an array of upward-looking acoustic Doppler current profilers (ADCP), the HFR-derived currents on the shelf are found to be consistent with ADCP currents, whereas along the shelf break, HFR-derived currents under-estimate ADCP currents at sites near Cape Hatteras, are roughly equal further to the southwest, and somewhat over-estimate ADCP currents north of Cape Hatteras.