Atmosphere Ocean Science Colloquium

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An Asymptotic Model for the Coupled Evolution of Near-Inertial Waves and Quasi-Geostrophic Flow

Speaker: Gregory Wagner, UCSD

Location: Warren Weaver Hall 1302

Date: Wednesday, April 27, 2016, 3:30 p.m.

Synopsis:

Far from boundaries, oceanic motion is primarily a mix of two modes: slowly-evolving eddies and currents, and more rapidly oscillating internal waves with near-inertial and tidal frequency. Here, we present a three-component asymptotic model which uses a multiple-scale asymptotic expansion to isolate the coupled evolution of near-inertial waves and quasi-geostrophic flow from the Boussinesq equations. A principal implication of the model is that near-inertial waves - which may be externally forced by winds, tides, or flow-topography interaction - can extract energy from mesoscale or submesoscale quasi-geostrophic flows. A second and separate implication of the model is that this wave-flow interaction catalyzes a loss of near-inertial energy to freely propagating near-inertial second harmonic waves with twice the inertial frequency. The newly-produced harmonic waves both propagate rapidly to depth and transfer energy back to the near-inertial wavefield at very small vertical scales. The upshot of second harmonic generation is a two-step mechanism whereby quasi-geostrophic flow catalyzes a nonlinear transfer of near-inertial energy to the small scales of wave breaking and mixing.