The large-scale features of the global ocean circulation and the sensitivity
of these features with respect to forcing changes are critically dependent upon
the influence of the mesoscale eddy field. One such feature, observed in
numerical simulations whereby the mesoscale eddy field is at least partially
resolved, is the phenomenon of eddy saturation, where the time-mean circumpolar
transport of the Antarctic Circumpolar Current displays relative insensitivity
to wind forcing changes. Coarse-resolution models employing the
Gent--McWilliams parameterisation with a constant Gent--McWilliams coefficient
seem unable to reproduce this phenomenon. In this article, an idealised model
for a wind-forced, zonally symmetric flow in a channel is used to investigate
the sensitivity of the circumpolar transport to changes in wind forcing under
different eddy closures. It is shown that, when coupled to a simple
parameterised eddy energy budget, the Gent--McWilliams coefficient of the form
described in Marshall et al. (2012) [A framework for parameterizing eddy
potential vorticity fluxes, J. Phys. Oceanogr., vol. 42, 539--557], which
includes a linear eddy energy dependence, produces eddy saturation as an
emergent property.Comment: 22 pages, 10 figures, Elsevier template, submitted to Ocean
Modelling; comments welcom