Abstract
Part I: Time evolving 2-D observations of near-surface flow with high frequency (HF) radar are well-suited for calculating Lagrangian Coherent Structures (LCSs) which are a valuable tool for observing turbulent flow. By comparing the evolving HF radar-derived LCS fields with satellite sea surface temperature imagery, the evolving structure of upwelling fronts, filaments, retention zones, and eddy-like recirculation are captured in the upwelling environment off the California coast. Part II: The inertial frequency is nearly diurnal at 30°N latitude which transects the northeastern Gulf of Mexico (NeGoM). At this latitude, near-surface inertial oscillations can amplify due to resonance with diurnal wind forcing. Diurnal oscillations have also been attributed to diurnal tidal forcing in this region. Because tidal forcing, wind forcing, and inertial oscillations are nearly diurnal, a unique series of comparative analyses are required to determine their relative influence on surface circulation. By comparing surface currents obtained by HF radar to predictions of the inertial response to wind forcing and barotropic tidal currents, it is found that diurnal oscillations in the NeGoM were predominantly due to wind-forced inertial oscillations in June 2010. The analyses provide a unique spatiotemporal perspective of inertial oscillations in the NeGoM where there is evidence of propagation, frequency and phase shifts, and amplitude variability. Positive (negative) sub-inertial vorticity ζ in the ocean shifts the effective inertial frequency feff of near-inertial oscillations (NIOs) above (below) the local inertial frequency f according to the relationship feff = f + ζ/2. It is found that NIO frequencies are consistent with feff determined from the vorticity field over the outer Mississippi Bight shelf and along the northern edge of the DeSoto Canyon during the last week of June 2010. Additionally, spatial NIO phase shifts associated with the frequency field of the NIOs are found to generate oscillatory divergence. In June 2010 oil from the Deepwater Horizon spill traversed through the NeGoM and it is speculated that the oil was exposed to mixing generated by the NIOs.