Atmosphere Ocean Science Colloquium

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The Life-Cycle of Wind Generated Near-Inertial Waves in Strong Ocean Fronts

Speaker: Dan Whitt, Stanford University

Location: Warren Weaver Hall 1302

Date: Wednesday, March 12, 2014, 3:30 p.m.

Synopsis:

The life-cycle of wind generated near-inertial waves in strong ocean fronts Abstract: The question of how wind-forced near-inertial waves interact with strongly baroclinic ocean fronts,such as wintertime western boundary currents, is investigated using theory, idealized numerical simulations, and observations. The investigation considers the full life-cycle of near-inertial waves in this context, including generation by atmospheric forcing, radiation from the boundary layer, propagation in the upper thermocline, blocking, trapping and amplification at internal turning points and critical layers, and ultimately wave breaking and dissipation there.Two key results emerge from this narrative: 1) although the dynamics of inertia-gravity wave propagation in strong fronts is qualitatively different from propagation in the absence of a background flow, the essential physics of near-inertial wave propagation can still be characterized by two conservation laws: i) conservation of absolute momentum, and ii) conservation of buoyancy. 2) The ubiquitous banded shear observed in the upper thermocline of the north wall front in the winter Gulf Stream over the course of a month-long observational campaign in the winter of 2012, leads to the conclusion that western boundary current fronts are undersea ?surf-zones? for near-inertial waves. That is, in the presence of strong and persistent atmospheric forcing, they are regions of persistently amplified wave shear, strong vertical velocities, enhanced turbulence and mixing.