gfdl on-line bibliography > 1988 citations
Particle dispersion and mixing of conservative properties in an eddy-resolving model
Böning, C. W., and M. D. Cox. 1988: Particle dispersion and
mixing of conservative properties in an eddy-resolving model. Journal
of Physical Oceanography, 18(2), 320-338.
Abstract: We examine the diffusive behavior of the flow field
in an eddy-resolving, primitive equation circulation model. Analysis of
fluid particle trajectories illustrates the transport mechanisms, which
are leading to uniform tracer and potential vorticity distributions in
the interior of the subtropical thermocline. In contrast to the assumption
of weak mixing in recent analytical theories, the numerical model indicates
the alternative of tracer and potential vorticity homogenization on isopycnal
surfaces taking place in a nonideal fluid with strong, along-isopycnal
eddy mixing.
The eastern, ventilated portion of the gyre appears to be sufficiently
homogeneous to allow the concept of an eddy diffusivity to apply. A break
in a random walk behavior of particle statistics occurs after about 100
days when along-flow dispersion sharply increases, indicative of mean shear
effects. During the first months of particle spreading, eddy dispersal
and mean advection are of similar magnitude. Eddy kinetic energy is if
O(60-80 cm2 s-2)
in the model thermocline, comparable to the pool of weak eddy intensity
found in the eastern parts of the subtropical oceans. Eddy diffusivity
in the model thermocline (Kxx = 8 x 107,
Kyy = 3 x 107
cm<2 s-1)
seems to be higher by a factor of about 3 than oceanic values estimated
for these areas. Below the thermocline, model diffusivity decreases substantially
and becomes much more anisotropic, with particle dispersal preferentially
in the zonal direction. The strong nonisotropic behavior, prominent also
in all other areas of weaker eddy intensity, appears as the major discrepancy
when compared with the observed behavior of SOFAR floats and surface drifters
in the ocean.