Surface M2 tidal currents along the North Carolina shelf observed with a high-frequency radar -: art. no. 3222

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 M-2 tidal current amplitudes ranged from 2 to 10 cm s(-1), with phases ranging from 100degrees to 120degrees, which compared well to previous results. Strong tidal current amplitudes and fine-scale variability occurred near bathymetric features. Decreasing M-2 surface tidal current amplitudes in the far field (similar to40 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 M-2 tidal currents over the shelf. Observed M-2 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.