M. Visbeck et al., SPECIFICATION OF EDDY TRANSFER-COEFFICIENTS IN COARSE-RESOLUTION OCEAN CIRCULATION MODELS, Journal of physical oceanography, 27(3), 1997, pp. 381-402
Parametric representations of oceanic geostrophic eddy transfer of hea
t and salt are studied ranging from horizontal diffusion to the more p
hysically based approaches of Green and Stone (GS) and Gent and McWill
iams (GM). The authors argue for a representation that combines the be
st aspects of GS and GM: transfer coefficients that vary in space and
time in a manner that depends on the large-scale density fields (GS) a
nd adoption of a transformed Eulerian mean formalism (GM). Recommendat
ions are based upon a two-dimensional (zonally or azimuthally averaged
) model with parameterized horizontal and vertical fluxes that is comp
ared to three-dimensional numerical calculations in which the eddy tra
nsfer is resolved. Three different scenarios are considered: 1) a conv
ective ''chimney'' where the baroclinic zone is created by differentia
l surface cooling; 2) spindown of a frontal zone due to baroclinic edd
ies; and 3) a wind-driven, baroclinically unstable channel. Guided by
baroclinic instability theory and calibrated against eddy-resolving ca
lculations, the authors recommend a form for the horizontal transfer c
oefficient given by k = alpha f/root Ri l(2) = alpha M(2)/N l(2), wher
e Ri = f(2)N(2)/M(4) is the large-scale Richardson number and f is the
Coriolis parameter; M(2) and N-2 are measures of the horizontal and v
ertical stratification of the large-scale flow, I measures the width o
f the baroclinic zone, and alpha is a constant of proportionality. In
the very different scenarios studied here the authors find alpha to be
a ''universal'' constant equal to 0.015, not dissimilar to that found
by Green for geostrophic eddies in the atmosphere. The magnitude of t
he implied k, however, varies from 300 m(2) s(-1) in the chimney to 20
00 m(2) s(-1) in the wind-driven channel.