A Study of Interactions Between Near-inertial Internal Waves and Mesoscale-to-Submesoscale Flows
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In this dissertation, we explore interactions between near-inertial internal waves (NIWs) and mesoscale-to-submesoscale flows. Three different topics under this broad subject are investigated using theoretical, numerical and observational approaches. The downward radiation of NIWs from the mixed layer to deep ocean in an idealized baroclinic geostrophic flow is theoretically analyzed based on the Young-Ben Jelloul (YBJ) equation. It is found that the dispersion of NIWs in the presence of baroclinic flow is achieved mainly through the phase separation among different horizontal and vertical modes. Both the eigen-frequency differences and mode-mode interferences contribute to the phase separation with the interferences locally in the modal space playing a much more dominant role than the nonlocal mode-mode interferences. Data from long-term mooring array and high-resolution numerical simulations in the Gulf of Mexico are used to analyze energy exchange between near-inertial internal waves and mesoscale eddies. Both the observations and numerical simulations reveal a permanent energy transfer from mesoscale eddies to NIWs below the mixed layer. In particular, this permanent energy transfer mainly occurs when the Okubo-Weiss (OW) parameter is positive. Further analysis suggests that the wave capture mechanism plays a key role in interactions between NIWs and mesoscale eddies. NIWs become highly anisotropic when the OW parameter is positive. The observed probability density function of propagation direction of NIWs is consistent with the predictions from the wave capture theory. Submesoscale O(<10 km) motions and their interactions with NIWs are studied theoretically and numerically using high-resolution numerical simulations. Submesoscale fronts (SMFs) with energetic vertical motions in the ocean interior are found to be closely associated with the NIWs. A dynamic mechanism for the SMF development in the presence of background NIWs is proposed. It shows that in convergence (downwelling) regions of NIWs, energy flux of the submesoscale motions converges and the energy is transferred from the NIWs to submesoscale motions, leading to enhanced submesoscale vertical velocity. The opposite is true in divergence (upwelling) zones of NIWs. The underlying dynamics can be understood in terms of wave action conservation of submesoscale motions in the presence of background NIWs.
Jing, Zhao (2016). A Study of Interactions Between Near-inertial Internal Waves and Mesoscale-to-Submesoscale Flows. Doctoral dissertation, Texas A & M University. Available electronically from