PUBLIC INTERFACE ~ PUBLIC DATA ~ PUBLIC ROUTINES ~ NAMELIST ~ DIAGNOSTIC FIELDS ~ ERROR MESSAGES ~ REFERENCES ~ NOTES

Module ocean_overexchange_mod

Contact:  S.M. Griffies
Reviewers: 
Change History: WebCVS Log

OVERVIEW

Exchange of tracer properties as dense shallow parcel discharged into deeper water to approach the depth of neutral buoyancy.

Exchange of tracer properties as dense shallow parcel is discharged into deeper water to approach the parcel's depth of neutral buoyancy. This module can be characterized as a mixture of the approach from Campin and Goosse (1999) and and dynamically determined xlandmix.

OTHER MODULES USED

       constants_mod
    diag_manager_mod
             fms_mod
     mpp_domains_mod
             mpp_mod
   ocean_density_mod
   ocean_domains_mod
ocean_parameters_mod
     ocean_types_mod
      ocean_util_mod
 ocean_workspace_mod

PUBLIC INTERFACE

ocean_overexchange_init:
overexchange:

PUBLIC DATA

None.

PUBLIC ROUTINES

  1. ocean_overexchange_init

    DESCRIPTION
    Initial set up for mixing of tracers into the abyss next to topography.


  2. overexchange

    DESCRIPTION
    Compute thickness and density weighted tracer source [tracer*rho*m/s] due to exchange of tracer properties in regions where density-driven overflows are favorable. Allow for exchanges to occur over horizontally distant points, so long as the dense shallow parcel finds that it will sit on the bottom of the horizontally adjacent columns. Doing so requires a search algorithm, which requires some if-test logic as well as extended halos. Note that the halos cannot be extended to larger than the size of the computational domain on a processor. This restriction limits the extent that we can search horizontally.

    This scheme can be characterized as a dynamical xlandmix based on the scheme of Campin and Goosse. The rates for the exchange are functions of the topographic slope and the density differences between parcels.



NAMELIST

&ocean_overexchange_nml

use_this_module
For using this module. Default use_this_module=.false.
[logical]
debug_this_module
For debugging
[logical]
do_bitwise_exact_sum
Set true to do bitwise exact global sum. When it is false, the global sum will be non-bitwise_exact, but will significantly increase efficiency. The default value is false.
[logical]
overexch_npts
Number of points used in search for the exchange method. Default overexch_npts=1. Note: it is not possible to have overexch_npts greater than or equal to the computational domain extents, as this would require updates across multiple processors. Default overexch_npts=1.
[integer]
overexch_weight_far
To place more weight on points further from central point. This may be done to enhance properties getting downslope. Default is overexch_weight_far=.false.
[logical]
overexch_width
Width of the re-weighting function used to emphasize the points further along in the search for exchange points. Default overexch_width=1.
[integer]
overexch_stability
Stability factor for determining the maximum overexch_flux. Default overexch_stability=0.25
[real]
overexch_min_thickness
Minimum bottom cell thickness allowed for use of this scheme. Have found that with very thin cells, the model can become very unstable. Default overexch_min_thickness=4.0
[real, units: metre]
overexch_check_extrema
Check to be sure there are no global tracer extrema formed due to the overexch process. Note that this approach DOES NOT conserve tracer, so it is not generally recommended. Default overexch_check_extrema=.false.
[logical]
overflow_mu
Dissipation rate for the bottom friction. Campin and Goosse suggest overflow_mu=10^-4
[real, units: sec^-1]
overflow_delta
Fraction of a grid cell participating in the overflow process. Campin and Goosse suggest overflow_delta=1/3.
[real, units: dimensionless]
overflow_umax
Maximum downslope speed used for determining the exchange rate. Default overflow_umax=1.0.
[real, units: m/s]

DATA SETS

None.

ERROR MESSAGES

None.

REFERENCES

  1. Campin and Goosse (1999): Parameterization of density-driven downsloping flow for a coarse-resolution model in z-coordinate", Tellus 51A, pages 412-430
  2. S.M. Griffies, M.J. Harrison, R. C. Pacanowski, and A. Rosati A Technical Guide to MOM4 (2003) NOAA/Geophysical Fluid Dynamics Laboratory
  3. S.M. Griffies, Elements of mom4p1 (2006) NOAA/Geophysical Fluid Dynamics Laboratory

COMPILER SPECIFICS

None.

PRECOMPILER OPTIONS

None.

LOADER OPTIONS

None.

TEST PROGRAM

None.

KNOWN BUGS

None.

NOTES

None.

FUTURE PLANS

None.

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