Abstract
Abstract. The importance of chaotic advection relative to turbulent diffusion is
investigated in an idealized model of a 3-D swirling and overturning ocean
eddy. Various measures of stirring and mixing are examined in order to
determine when and where chaotic advection is relevant. Turbulent diffusion
is alternatively represented by (1) an explicit, observation-based,
scale-dependent diffusivity, (2) stochastic noise, added to a deterministic
velocity field, or (3) explicit and implicit diffusion in a spectral numerical
model of the Navier–Stokes equations. Lagrangian chaos in our model occurs only
within distinct regions of the eddy, including a large chaotic “sea” that
fills much of the volume near the perimeter and central axis of the eddy and
much smaller “resonant” bands. The size and distribution of these regions
depend on factors such as the degree of axial asymmetry of the eddy and the
Ekman number. The relative importance of chaotic advection and turbulent
diffusion within the chaotic regions is quantified using three measures: the
Lagrangian Batchelor scale, the rate of dispersal of closely spaced fluid
parcels, and the Nakamura effective diffusivity. The role of chaotic
advection in the stirring of a passive tracer is generally found to be most
important within the larger chaotic seas, at intermediate times, with
small diffusivities, and for eddies with strong asymmetry. In contrast, in
thin chaotic regions, turbulent diffusion at oceanographically relevant rates
is at least as important as chaotic advection. Future work should address
anisotropic and spatially varying representations of turbulent diffusion for
more realistic models.
Funder
Division of Ocean Sciences
Office of Naval Research
Reference70 articles.
1. Abernathey, R., Marshall, J., Mazloff, M., and Shuckburgh, E.: Enhancement of
mesoscale eddy stirring at steering levels in the Southern Ocean, J.
Phys. Oceanogr., 40, 170–184, 2010. a
2. Aref, H.: Stirring by chaotic advection, J. Fluid Mech., 143,
1–21, 1984. a
3. Branicki, M. and Kirwan Jr., A.: Stirring: the Eckart paradigm revisited,
Int. J. Eng. Sci., 48, 1027–1042, 2010. a
4. Brett, G.: 3D rotating cylinder eddy codes,
https://doi.org/10.5281/zenodo.1560663, 2018. a
5. Brett, G. and Wang, P.: 3D rotating cylinder eddy data,
https://doi.org/10.5281/zenodo.1560204, 2018. a
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