Publication Date:
2022-05-25
Description:
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2003
Description:
Inertial terms dominate the single-gyre ocean model and prevent western-intensification
when the viscosity is small. This occurs long before the oceanically-appropriate parameter
range. It is demonstrated here that the circulation is controlled if a mechanism
for ultimate removal of vorticity exists, even if it is active only in a narrow
region near the boundary.
Vorticity removal is modeled here as a viscosity enhanced very near the solid
boundaries to roughly parameterize missing boundary physics like topographic interaction
and three dimensional turbulence over the shelf. This boundary-enhanced
viscosity allows western-intensified mean flows even when the inertial boundary width,
is much wider than the frictional region because eddies flux vorticity from within the
interior streamlines to the frictional region for removal.
Using boundary-enhanced viscosity, western-intensified calculations are possible
with lower interior viscosity than in previous studies. Interesting behaviors result: a
boundary-layer balance novel to the model, calculations with promise for eddy parameterization,
eddy-driven gyres rotating opposite the wind, and temporal complexity
including basin resonances.
I also demonstrate that multiple-gyre calculations have weaker mean circulation
than single-gyres with the same viscosity and subtropical forcing. Despite traditional
understanding, almost no inter-gyre flux occurs if no-slip boundary conditions are
used. The inter-gyre eddy flux is in control only with exactly symmetric gyres and
free slip boundaries.
Even without the inter-gyre flux, the multiple-gyre circulation is weak because
of sinuous instabilities on the jet which are not present in the single-gyre model.
These modes efficiently flux vorticity to the boundary and reduce the circulation
without an inter-gyre flux, postponing inertial domination to much smaller viscosities.
Then sinuous modes in combination with boundary-enhanced viscosity can control
the circulation.
Keywords:
Eddies
;
Turbulent boundary layer
;
Ocean-atmosphere interaction
;
Mathematical models
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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