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Module ocean_sigma_diffuse_mod

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


OVERVIEW

Thickness weighted time tendency for tracer from sigma diffusion model grid cells.

This module computes the thickness weighted time tendency for tracer arising from Laplacian diffusion within the bottom-most model grid cells. The diffusivity used to determine the strength of the tendency is generally set to be a function of the local horizontal grid spacing. Diffusivity is the sum of an a priori background plus a velocity dependent diffusivity. It is large if there is a heavier parcel living adjacent within the "sigma layer" above a lighter parcel. It is small otherwise.

The thickness of the "sigma layer" is time independent and equated to the thickness of the bottom partial cell thickness dht.

When the logical sigma_tracer_diffusion=.true., other diffusive fluxes passing across bottom cell boundaries are masked to zero. Generally, sigma_tracer_diffusion=.false. has been found useful.


OTHER MODULES USED

      constants_mod
diag_manager_mod
fms_mod
mpp_domains_mod
mpp_mod
ocean_domains_mod
ocean_density_mod
ocean_operators_mod
ocean_types_mod

PUBLIC INTERFACE

ocean_sigma_diffuse_init:
sigma_diffusion:


PUBLIC DATA

None.


PUBLIC ROUTINES

  1. ocean_sigma_diffuse_init

    DESCRIPTION
    Initialize the sigma diffusion module by registering fields for diagnostic output and performing some numerical checks to see that namelist settings are appropriate.


  2. sigma_diffusion

    DESCRIPTION
    This subroutine computes the thickness weighted time tendency for tracer from sigma diffusion and stores result in trace th_tendency.



NAMELIST

&ocean_sigma_diffuse_nml

sigma_diffuse_on
Must be true to use this module.
[logical]
tmask_sigma_on
IF .true. then masks out fluxes passing into the sigma layer, except those associated with sigma diffusion. Typically set to .false.
[logical]
sigma_diffusivity
Sigma tracer diffusivity for use if not using micom diffusivity.
[real, units: m^2/sec]
sigma_diffusivity_ratio
When flow along sigma surface is stable (i.e., heavy parcels are below lighter parcels) then sigma diffusivity is reduced by sigma_diffusivity_ratio from the case where heavy parcels are above lighter parcels.
[real, units: dimensionless]
sigma_thickness_max
The maximum thickness of the bottom sigma diffusion layer. If dht > sigma_thickness_max, then bbl_thickness is set to sigma_thickness_max. Otherwise, bbl_thickness=dht.
[real, units: meter]
tracer_mix_micom
If .true., then the sigma diffusivity is set according to a velocity scale times the grid spacing.
[logical]
vel_micom
Velocity scale that is used for computing the MICOM diffusivity.
[real, units: m/sec]


DATA SETS

None.


ERROR MESSAGES

None.


REFERENCES

  1. R. Doscher and A. Beckmann Effects of a bottom boundary layer parameterization in a coarse-resolution model of the North Atlantic Ocean Journal of Atmospheric and Oceanic Technology (1999), vol 17 pages 698--707
  2. A. Beckmann and R. Doscher", A method for improved representation of dense water spreading over topography in geopotential--coordinate models Journal of Physical Oceanography (1997) vol 27, pages 581--59
  3. S.M. Griffies, M.J. Harrison, and A. Rosati, A Guide to MOM4 for Users and Developers (2002)


COMPILER SPECIFICS

None.


PRECOMPILER OPTIONS

None.


LOADER OPTIONS

None.


TEST PROGRAM

None.


KNOWN BUGS

None.


NOTES

The numerical implementation requires no calls to mpp_update_domains.


FUTURE PLANS

None.


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