3.6.1 Parameters: Computational domain, geometry and time-discretization

dimensions

The number of points in the x, y, and r directions are represented by the variables sNx, sNy and Nr respectively which are declared and set in the file model/inc/SIZE.h. (Again, this assumes a mono-processor calculation. For multiprocessor calculations see the section on parallel implementation.)

grid

Three different grids are available: cartesian, spherical polar, and curvilinear (which includes the cubed sphere). The grid is set through the logical variables usingCartesianGrid, usingSphericalPolarGrid, and usingCurvilinearGrid. In the case of spherical and curvilinear grids, the southern boundary is defined through the variable ygOrigin which corresponds to the latitude of the southern most cell face (in degrees). The resolution along the x and y directions is controlled by the 1D arrays delx and dely (in meters in the case of a cartesian grid, in degrees otherwise). The vertical grid spacing is set through the 1D array delz for the ocean (in meters) or delp for the atmosphere (in Pa). The variable Ro_SeaLevel represents the standard position of Sea-Level in ``R'' coordinate. This is typically set to 0m for the ocean (default value) and 10 Pa for the atmosphere. For the atmosphere, also set the logical variable groundAtK1 to '.TRUE.' which puts the first level (k=1) at the lower boundary (ground).

For the cartesian grid case, the Coriolis parameter is set through the variables f0 and beta which correspond to the reference Coriolis parameter (in s ) and (in m s ) respectively. If beta is set to a nonzero value, f0 is the value of at the southern edge of the domain.

topography - full and partial cells

The domain bathymetry is read from a file that contains a 2D (x,y) map of depths (in m) for the ocean or pressures (in Pa) for the atmosphere. The file name is represented by the variable bathyFile. The file is assumed to contain binary numbers giving the depth (pressure) of the model at each grid cell, ordered with the x coordinate varying fastest. The points are ordered from low coordinate to high coordinate for both axes. The model code applies without modification to enclosed, periodic, and double periodic domains. Periodicity is assumed by default and is suppressed by setting the depths to 0m for the cells at the limits of the computational domain (note: not sure this is the case for the atmosphere). The precision with which to read the binary data is controlled by the integer variable readBinaryPrec which can take the value 32 (single precision) or 64 (double precision). See the matlab program gendata.m in the input directories under verification to see how the bathymetry files are generated for the case study experiments.

To use the partial cell capability, the variable hFacMin needs to be set to a value between 0 and 1 (it is set to 1 by default) corresponding to the minimum fractional size of the cell. For example if the bottom cell is 500m thick and hFacMin is set to 0.1, the actual thickness of the cell (i.e. used in the code) can cover a range of discrete values 50m apart from 50m to 500m depending on the value of the bottom depth (in bathyFile) at this point.

Note that the bottom depths (or pressures) need not coincide with the models levels as deduced from delz or delp. The model will interpolate the numbers in bathyFile so that they match the levels obtained from delz or delp and hFacMin.

(Note: the atmospheric case is a bit more complicated than what is written here I think. To come soon...)

time-discretization

The time steps are set through the real variables deltaTMom and deltaTtracer (in s) which represent the time step for the momentum and tracer equations, respectively. For synchronous integrations, simply set the two variables to the same value (or you can prescribe one time step only through the variable deltaT). The Adams-Bashforth stabilizing parameter is set through the variable abEps (dimensionless). The stagger baroclinic time stepping can be activated by setting the logical variable staggerTimeStep to '.TRUE.'.

Copyright © 2006 Massachusetts Institute of Technology

Last update 2011-01-09