Dr. Jennifer MacKinnon
Scripps Institution of Oceanography
University of California, San Diego
858-822-3716
Research Projects
(Click on title for detailed description and results)
Numerical simulations of energy transfer between internal waves.
Using a pseudo-spectral numerical model, we investigate how energy is drained from a propagating internal tide, as well as more general question of how energy flows from large to small scales in the ocean. The most dramatic result is that fast parametric subharmonic responsibility is able to quickly transfer energy from a propagating internal tide to smaller-scale waves of near half the frequency. This transfer is larger than suggested from previous theoretical results, most likely due to the typical coherence of internal tides. The effect is only possible equatorward of 29 N or S, and becomes particular efficient right at this latitude.
Numerical Investigations of Currents, Eddy Kinetic Energy, and Internal waves in the Southern Ocean (NICKELS)
My thesis work with Mike Gregg explored the magnitude and mechanisms of turbulent mixing on the New England shelf. Data was collected in two cruises in the summer of 1996 and the spring of 1997. Results showed clear delineationg of mixing in surface and bottom boundary layers, driven by boundary friction and wind mixing, and that in the stratified region in between, driven by internal wave breaking. In the summer, over half of the internal wave induced mixing was associated with the passage of episodic strongly nonlinear solitons, pictured at right. Click on the title to learn more.
Diapyncal mixing in the Southern Ocean (SO) plays a vital role in controlling the global overturning circulation that redistributes heat, freshwater, and dissolved greenhouse gases throughout the world's oceans. In particular, internal lee waves generated by mean and eddy flow over rough topography in the Southern Ocean may propagate upwards and dump their momentum into critical layer absorption, much as mountain waves do in the atmosphere. This in turn may play an important (and under-appreciated) role in the residual mean circulation momentum budget of the ACC. To investigate these notions, I am conducting a series of idealized numerical experiments. The experiments impose an upward propagating field of internal waves, consistent with various models of wave generation, onto a realistic mean zonal flow and geostrophic eddy field. Stay tuned for preliminary results...
In the meantime, check out the excellent PhD work of Andy Thompson investigating the magnitude and patterns of turbulent mixing in the Drake passage [thompson_etal_07.pdf]
Langmuir Cells and Internal Waves at the mixed-layer base.
Recent observational and theoretical evidence suggests that there may be dynamical interaction between Langmuir cells in the ocean mixed layer and internal waves propagating in the stratified region beneath. Jeff Polton is doing postdoctoral work with Jerome Smith and myself to investigate this possibility with Large-Eddy-Simulation (LES) numerical models. He and our previous postdoc, Andres Tejada-Martinez, have designed a new LES model to include both Craik-Leibovich Langmuir forcing of an unstratified mixed layer and a stratified ‘transition zone’ beneath. Preliminary results show that perturbations of the mixed layer base by energetic Langmuir Cells create high-frequency internal waves that propagate downwards. These waves may be an important source of mixing in the stratified transition zone, which in turn is vital for regulating exchange of heat, dissolved gasses, and nutrients between the surface and deep ocean. The first paper for this project has just been accepted for publication in GRL - see Publications page for a preprint download.
In the spring of 2006 we chased the internal tide north from Hawaii to 37 N with two cruises aboard the R/V Revelle. Preliminary results indicate that that (i) PSI occurs in the ocean with sufficient intensity to fundamentally alter the ocean internal wave field at and equatorward of the critical latitude, but (ii) appears not to represent a significant energy sink for the internal tide.
Recent evidence from Kunze et al 06 (figure below) suggests turbulence above the South-west Indian Ridge is among the strongest in the entire Indian Ocean basin. This strong mixing may be due both to locally generated internal tides and scattering of low-mode near-inertial waves generated due south in the windy Southern Ocean. Two cruises were successfully completed in the winter of 07/08. Click on the title for details and preliminary results...