Coastal ocean response to near-resonant sea breeze/land breeze near the critical latitude in the Georgia Bight

On the mid- to outer shelf of the Georgia Bight, surface-intensified non-tidal diurnal currents can exceed 25 cm/s more than 120 km offshore, with currents in a lower layer 180°out of phase upper layer currents. Persistent from April through October, these diurnal motions appear to be inertial oscillations and near-inertial internal waves, forced by sea breeze/land breeze (SBLB) and other diurnal winds, resonant with the inertial frequency at 30°N or S.;Observational wind and current data from 1999-2007 are analyzed from a moored array in the Georgia Bight, between 29-32°N, where linear theory predicts maximum SBLB magnitude and offshore extent. Complex empirical orthogonal function analysis is used to separate non-tidal diurnal/inertial currents from the tidal currents at frequencies that cannot be simultaneously resolved at relevant time scales. The spatial structure, variability, and phase of diurnal/inertial currents are described and compared to those of SBLB as both the atmospheric forcing and ocean response pass through the critical latitude for diurnal/inertial resonance. Diurnal variance of observed and modeled winds indicate SBLB winds on the order of 1-2 m/s at least 250 km offshore, nearly an order of magnitude greater than the anticipated offshore scale.;The magnitude of coastal ocean response is strongly controlled by the interaction of bottom friction and stratification, and increases with distance offshore, producing diurnal/inertial divergence/convergence over the inner to mid-shelf. Examination of shear and stratification on the mid- to outer shelf reveals that the pycnocline partially decouples the water column. The level of maximum shear bounds rather than coincides with the pycnocline, which contains a sub-surface jet that rotates anticyclonically but is 180° out of phase with the directly-forced surface currents. The vertical structure of the currents is not-well represented by models that describe the vertical structure observed elsewhere, and more closely resembles a three-layer structure: a wind-forced surface layer overlying a stratified inertial jet layer and a well-mixed quiescent bottom layer. The vertical structure and its variability has significant implications for mixing, as the shelf of the Georgia Bight appears to trap near-inertial energy input from the wind, enhanced near the critical latitude for diurnal/inertial resonance.