Hunter Elias (Rutgers University, USA)

An extensive CODAR HF-radar network has been acquiring observations of surface currents in the Mid Atlantic Bight (MAB) continental shelf ocean for several years. The fundamental CODAR observation is the component of surface current (nominally ~2 m below sea surface) in the radial direction of view from a single antenna, geo-located by range and azimuth. Surface velocity vectors are computed by combining radials observed by multiple sites. We exploit the concave geometry of the MAB coastline and the many possible radial views from numerous antennae to select transects that are substantially along or across isobaths, and compute wavenumber spectra for both along-shelf and across-shelf components of velocity. Comparing spectra computed from radial velocities to spectra for the same vector component extracted from the total vectors we find that the optimal interpolation combiner significantly damps energy for wavenumbers exceeding 0.03 km^-1. This has ramifications for our error model in 4DVAR assimilation of CODAR total velocity. We further computed wavenumber spectra for altimeter SSHA from CryoSat-2 for ensembles of tracks in the same region of the MAB that were predominantly across- or along-shelf. Velocity spectra exhibit power law dependence close to k^-5/3 down to the limit of resolution, while SSHA spectra are somewhat steeper. The constraint that bathymetry exerts on circulation on this broad, shallow shelf could influence the spectral characteristics of variability, as could winter well mixed versus summer strongly stratified conditions. Velocity and SSHA spectra are being compared to spectral estimates from model simulations as a rigorous assessment of convergence of the model resolution, and to explore theories of surface quasi-geostrophic turbulence that might explain the observed spectral characteristics.