Meeting Abstracts
On Multi-Scale Dispersion under the Influence of Surface Mixed Layer Instabilities and Deep Flows
Tamay Ozgokmen, Andrew Poje, Paul Fischer, Hank Childs, Harinarayan Krishnan, Christoph Garth, Angelique Haza, Edward Ryan
RSMAS, University of Miami
(Abstract received 05/14/2012 for session D)
ABSTRACT
A series of large eddy simulations is used to assess the transport properties of multi-scale ocean
flows. In particular, we compare scale-dependent measures of Lagrangian relative dispersion and the
evolution of passive tracer releases in models containing only submesoscale mixed layer instabilities and
those containing mixed layer instabilities modified by deeper, baroclinic mesoscale disturbances. Visualization
through 3D finite-time Lyapunov exponents
and spectral analysis show that the small scale instabilities of the mixed layer rapidly lose coherence in the
presence of larger-scale straining induced by the mesoscale motion. Eddy diffusivities computed from passive tracer
evolution increase by an order of magnitude as the flow transitions from small to large scales. During the time
period when both instabilities are present, scale-dependent relative Lagrangian dispersion, given by the finite-scale Lyapunov
exponent (FSLE), shows two distinct plateau regions clearly associated with the disparate instability scales. In this case,
the maximum value of FSLE over the submesocales at the surface flow is three times greater than
FSLE at the mixed layer base, which is under the influence of deeper baroclinic motions.
The implication of this result is that for problems involving prediction of the dispersion of surface particles,
parameterizations would be needed in models that do
not explicitly resolve submesoscale turbulent features.