We study the development of mean structures in a nonlinear model of large
scale ocean dynamics with bottom topography and dissipation, and forced with a
noise term. We show that the presence of noise in this nonlinear model leads
to persistent average currents directed along isobaths. At variance with
previous works we use a scale unselective dissipation, so that the phenomenon
can not be explained in terms of minimum enstrophy states. The effect requires
the presence of both the nonlinear and the random terms, and can be though of
as an ordering of the stochastic energy input by the combined effect of
nonlinearity and topography. The statistically steady state is well
described by a generalized canonical equilibrium with mean energy and
enstrophy determined by a balance between random forcing and dissipation. This
result allows predicting the strengh of the noise-sustained currents.
Finally we discuss the relevance that these noise-induced currents could have
on real ocean circulation.
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