Abstract
Salt fingers occur throughout a large fraction of the World Ocean and
can have substantial effects on large-scale mixing processes, such as
the Meridional Overturning Circulation (see, e.g., Zhang et al., 1998).
However, most numerical and laboratory studies of this phenomenon occur
in quiescent environments. We simulate salt fingers in the presence of
constant and oscillating shear in order to quantify the mixing of heat
and salt by these systems under the impacts of large-scale internal
waves. The code used in these simulations (the “Rocking Ocean Modeling
Environment” or ROME) is a new pseudo-spectral hydrodynamic model which
incorporates a steady or oscillatory background shear flow with a
spatially uniform background velocity gradient. This configuration
presents a challenge for modeling via Fourier-based algorithms because
the typical evolution of such a flow is incompatible with the periodic
boundary conditions at the vertical extremities of the computational
domain. This complication is addressed by reformulating the governing
equations in a new, temporally varying “tilting” coordinate system
associated with the background flow as has been done in the past in the
field of homogenous turbulence. Generally, it is shown that the
application of shear can reduce fluxes by a factor of 2 or 3 for typical
amplitudes of near-inertial waves and that the impact of shear decreases
as the frequency of the applied shear increases. Though the focus of
this study is on the effects of shear on double-diffusive systems, ROME
is well-suited to a wide range of problems involving sheared stratified
systems.