Ng. Hogg, TOWARD PARAMETERIZATION OF THE EDDY FIELD NEAR THE GULF-STREAM, Deep-sea research. Part 1. Oceanographic research papers, 40(11-12), 1993, pp. 2359-2376
Analysis of measurements from two long-term moored arrays in and near
the Gulf Stream suggests a simple parameterization of eddy spatial cov
ariance statistics: a parameterization that can be referred to as ''qu
asi-homogeneous and isotropic''. Taking the normalized covariance func
tion (i.e. the correlation function) for streamfunction to be homogene
ous and isotropic and assuming motions to be horizontally nondivergent
and hydrostatic permit the velocity and temperature covariances to be
derived from the streamfunction covariance. Statistical tests indicat
e that deviations from these assumptions are indistinguishable from Ga
ussian random noise. The spatial correlation function used is Gaussian
with a decay scale of about 140 km, which is only weakly depth depend
ent. A simple form is also suggested for the vertical lag dependence.
This parameterization permits calculation of derived quantities such a
s the eddy vorticity flux divergence which is discussed in the context
of the mean potential vorticity balances for the depth integrated cir
culation and for the subthermocline layer. The divergence of the relat
ive vorticity flux is found capable of driving two counter-rotating gy
res of strength 30-40 Sv on either side of the Stream, as are observed
. The ''thickness flux'' dominates the lower layer eddy potential vort
icity flux and is of the correct sign to make the recirculation more b
arotropic. The lower layer eddy forcing is weak and the gyres exist in
a region of nearly uniform mean potential vorticity.