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Exact, conservative reconciliation of the external and internal estimates of the free surface height.
Robert Hallberg, Alistair Adcroft
NOAA/GFDL and Princeton University
(Abstract received 07/20/2007 for session X)
ABSTRACT
When ocean models use a split time stepping scheme for the barotropic and baroclinic modes, they generate two distinct estimates of the free surface height - one from the external barotropic solver and the other from the vertical integral of the interior continuity equations. In layered models, these are difficult to reconcile because of the necessarily nonlinear continuity solvers that must be used to maintain positive definite layer thicknesses. The external estimate more accurately captures external gravity wave adjustment, while the internal estimate gives exact conservation of tracers. This talk presents a novel solution for exactly and conservatively reconciling these two estimates, based on a rapidly converging iterative adjustment of the time-mean barotropic acceleration used in the interior layers\' continuity equations. The effects of vertical viscosity need to be considered in these iterations to avoid exciting unphysical abyssal flows around topography. When a piecewise parabolic method approach is used for the continuity equations, this approach is shown to be quite computationally affordable.
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2007 LOM Workshop, Bergen, Norway, August 20-22, 2007