[GTP] Fwd: GTP Seminar May 6, 2013

[Carolyn Mueller]

GTP Seminar

AN OCEANIC ULTRA-VIOLET CATASTROPHE, WAVE-PARTICLE DUALITY AND A
STRONGLY NONLINEAR CONCEPT OF GEOPHYSICAL TURBULENCE
Kurt Polzin
  Woods Hole Oceanographic Institution

Monday, May 6, 2013
Mesa Lab Main Seminar Room
Lecture at 3:30pm

Nonlinear interactions between high frequency internal waves interacting
with larger vertical and horizontal scale waves having inertial
frequency are investigated using ray tracing techniques, analytic
approximations to kinetic equations, solutions for the moments of a
diffusive approximation to the resonant kinetic equation and Taylor's
identity for relative dispersion.  Tracing high frequency waves in one
and two inertial wave backgrounds demonstrates that the infinitesimal
amplitude and finite amplitude limits are phenomenologically distinct:
the finite amplitude state is characterized by the coalescing of the two
small scale members of the triad and a transition to a bound wave
phenomena.  This coalescence marks the transition from the coupled
oscillator paradigm to a particle (wave packet) in a potential well
paradigm. Tracing high frequency waves in stochastic inertial wave
backgrounds does not reveal any such transition.  Rather, the ray
tracing results are phenomenologically consistent with the particle in a
(stochastic) well paradigm, independent of amplitude.

Tracing high frequency waves in a stochastic background of inertial
oscillations also provides estimates of the temporal evolution for the
ensemble mean and variance of vertical wavenumber of a test wave
distribution.  These estimates are compared to the evolution of the
first and second moments of a diffusive approximation to the resonant
kinetic equation.  The diffusive closure manages to describe the
evolution of the first two moments at energy levels an order of
magnitude smaller than background oceanic values and predicts {\em no}
transport of action to smaller scales.  At realistic energy levels the
growth of the second moment is inhibited relative to the first, implying
a finite downscale action transport.  We demonstrate using Taylor's
identity for relative dispersion that the transition occurs when the
interaction timescale becomes smaller than the decorrelation time scale
of the interaction process.  We argue that the action transport in this
parameter regime is the averaged product of particle size (action
density) and velocity (time rate of change of the first moment).  This
concept is the genesis for the heuristically motivated Finescale
Parameterization which summarizes current knowledge relating turbulent
dissipation to finescale internal wave spectra.



-- 
Carolyn Mueller
NCAR IMAGe
1850 Table Mesa Drive
Boulder, CO 80305
http://www2.image.ucar.edu/
Tel: 303 497-2491
Fax: 303-497-2483