| Abstract: Mesoscale eddies in the ocean play an
important role in the ocean circulation. In order to simulate the ocean
circulation, mesoscale eddies must be included explicitly or parameterized.
The eddy permitting calculations of the Los Alamos ocean circulation model
offer a special opportunity to test aspects of parameterizations that have
recently been proposed. Although the calculations are for a model in level
coordinates, averages over a five-year period have been carried out by
interpolating to instantaneous isopycnal surfaces. The magnitude of "thickness
mixing" or bolus velocity is found to coincide with areas of intense
mesoscale activity in the western boundary currents of the Northern Hemisphere
and the Antarctic Circumpolar Current. The model also predicts relatively
large bolus fluxes in the equatorial region. The analysis does show that
the rotational component of the bolus velocity is significant. Predictions
of the magnitude of the bolus velocity, assuming downgradient mixing of
thickness with various mixing coefficients, have been compared directly
with the model. The coefficient proposed by Held and Larichev provides
a rather poor fit to the model results because it predicts large bolus
velocity magnitudes at high latitudes and in other areas in which there
is only a small amount of mesoscale activity. A much better fit is obtained
using a constant mixing coefficient or a mixing coefficient originally
proposed by Stone in a somewhat different context. The best fit to the
model is obtained with a coefficient proportional to lambda²
/tau, where lambda is the radius of deformation, and tau
is the Eady timescale for the growth of unstable baroclinic waves. |