Module ocean_sigma_diffuse_mod
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
PUBLIC DATA
None.
PUBLIC ROUTINES
-
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.
-
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
- 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
- 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
- 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.