Introduction and Model Description

The original Gent-Cane model (Gent and Cane, 1989) was developed for modeling the equatorial pacific on a stretched longitude/latitude A-grid. Fourth order approximations to horizontal spatial derivatives combined with a fourth order (in time) Lorenz cycle provided a high order discretization advantageous for high resolution runs. The original vertical structure was simply a mixed layer at the surface and sigma layers down to a bottom layer of no motion. The surface mixed layer could be either a true layer with no mass exchange with lower layers, or could be kept at a fixed thickness. Restoration of SST at the surface provided the surface heat flux and Shapiro filters, reducing the order near land boundaries, provided a minimal amount of horizontal diffusion. The vertical diffusion of momentum and heat was explicit.

Most of the horizontal features have been kept in the present version. The 4th order time and space (horizontal) discretization has been maintained, the Shapiro filters (reduced, conservative, narrow passage modifications,...) are still used, and most of the old options remain. The only major exception is that the reduced gravity setup (assuming no motion at depth) is not currently supported in this version (but easily could be, if the need arises ...).

Descriptions of most of the features of the current model can be found in Keith Rodger's documentation. The major changes from the original Gent/Cane model are the vastly improved I/O handling, a barotropic solver, a new ocean mixed layer parameterization and an atmospheric mixed layer (AML). The I/O utilities, written by Senya Basin, include

Naomi Naik's barotropic solver allows the model to be run with a constant bathymetry assumption rather than the reduced gravity assumption. Vertical mixing has been generalized to use a combination of convective adjustment with a Kraus-Turner parameterization of wind mixing and Richardson number dependent mixing , the Large et al. K-profile parameterisation (KPP) , or Dake Chen 's ocean hybrid vertical mixing scheme . As either an alternative or in addition to the Shapiro filter, Isopycnal diffusion has been added, with an option to make it purely isopycnal or horizontal. The Gent-McWilliams eddy parameterization is also available, with variable coefficient as suggested by Visbeck et al. Density is computed from both temperature and salinity by a computationally efficient high order approximation to the UNESCO formula, and passive tracers can be implemented by specifying initial conditions in a user supplied data file. Richard Seager's atmospheric mixed layer (AML) computes the surface fluxes rather than restoration to SST and SSS, with data files prescribing wind, air temperature and humidity over land, clouds, solar radiation and precipitation. Thermodynamic ice has been added by Bob Newton and Martin Visbeck as an integral part of the AML. Ice advection has been coded, but has not been tested.