Surface M2 tidal currents along the North Carolina shelf observed with a high‐frequency radar

Abstract

Surface tidal circulation over the continental shelf of Duck, North Carolina, was explored using surface current observations measured by a high‐frequency (HF) radar. The Ocean Surface Current Radar (OSCR) was deployed at the U.S. Army Corps of Engineers (USACE) Field Research Facility (FRF) in Duck, North Carolina, during 1–30 October 1994 and measured surface current at 20‐min intervals at 700 cells with a 1.2‐km resolution in a 25 × 44 km domain. Harmonic analysis of the surface current indicates fine‐scale (O(1 km)) variability in tidal amplitudes and phases within the study domain. The M2 tidal current amplitudes ranged from 2 to 10 cm s−1, with phases ranging from 100° to 120°, which compared well to previous results. Strong tidal current amplitudes and fine‐scale variability occurred near bathymetric features. Decreasing M2 surface tidal current amplitudes in the far field (∼40 km) of the radar domain are consistent with decreasing spectral quality of the HF radar returns. A 1‐D barotropic tidal model is utilized to examine the physics of the M2 tidal currents over the shelf. Observed M2 tidal currents compare well with those predicted by the model over the inner shelf to the midshelf. However, differences between the observed and the barotropic tidal currents of 5–8 cm s−1 are related to the decrease in spectral quality of the HF radar data in the far field.