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

Module ocean_bih_friction_mod

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


OVERVIEW

This module computes thickness weighted time tendency for horizontal velocity arising from horizontal biharmonic friction.

This module computes thickness weighted time tendency for horizontal velocity arising from horizontal biharmonic friction. The viscosity used to determine the strength of the tendency can be a general function of space and time as specified by the Smagorinsky approach as well as a grid-scale dependent background viscosity. The form of the friction operator can be isotropic or anisotropic in the horizontal plane.


OTHER MODULES USED

      constants_mod
diag_manager_mod
fms_mod
mpp_domains_mod
mpp_mod
ocean_domains_mod
ocean_operators_mod
ocean_types_mod

PUBLIC INTERFACE

ocean_bih_friction_init:
horz_bih_friction:
BDX_EU_smag:
BDY_NU_smag:
horz_bih_viscosity_check:
horz_bih_reynolds_check:


PUBLIC DATA

None.


PUBLIC ROUTINES

  1. ocean_bih_friction_init

    DESCRIPTION
    Initialize the horizontal biharmonic friction module by registering fields for diagnostic output and performing some numerical checks to see that viscosity is set appropriately.


  2. horz_bih_friction

    DESCRIPTION
    This function computes the time tendency for horizontal velocity (i.e., the acceleration) from horizontal biharmonic friction. The algorithm is derived from a functional approach that ensures kinetic energy is consistenty dissipated for all flow configurations. The triad do-loops are expanded in order to enhance the ability of cache-based machines to keep most of the variables on-cache.

    Fundamental to the scheme are the rates of horizontal deformation
    horizontal tension = DT = (dy)(u/dy)_x - (dx)(v/dx)_y
    horizontal strain = DS = (dx)(u/dx)_y + (dy)(v/dy)_x
    Units of the tension and strain are sec^-1.

    Four tensions and four strains are computed for each velocity point,
    corresponding to the four triads surrounding the point.
    The following notation is used to distinguish the triads:
    (0,1)=northwest triad (1,1)=northeast triad,
    (0,0)=southwest triad, (1,0)=southeast triad

    A triad contributes when at least one of its velocities is not a land point. In order to obtain the correct tension and strain next to boundaries, tension and strain should not be masked with umask.

    As shown in Griffies and Hallberg (2000), a biharmonic operator with a nonconstant viscosity is guaranteed to dissipate kinetic energy *only* when using the sqrt of the biharmonic viscosity at each of the two stages of the algorithm. The sqrt approach is employed here.



  3. BDX_EU_smag

    DESCRIPTION
    Compute backwards Derivative in X of a quantity defined on the east face of a U-cell. Slightly modified version of BDX_EU used in ocean_operators.F90. If input is a(i,j) then output is defined at (i-1/2,j).

    BDX_EU_smag changes dimensions by m^-3


    INPUT
    a    field defined on the east face of a U-cell
       [real, dimension(isd:ied,jsd:jed)]

  4. BDY_NU_smag

    DESCRIPTION
    Compute backwards Derivative in Y of a quantity defined on the north face of a U-cell. Slightly modified version of BDY_EU used in ocean_operators.F90. If input is a(i,j) then output is defined at (i,j-1/2).

    BDY_EU_smag changes dimensions by m^-3


    INPUT
    a    field defined on the north face of a U-cell
       [real, dimension(isd:ied,jsd:jed)]

  5. horz_bih_viscosity_check

    DESCRIPTION
    Subroutine to perform linear stability check for the biharmonic operator given a value for the horizontal biharmonic viscosity.


  6. horz_bih_reynolds_check

    DESCRIPTION
    Subroutine to compute the biharmonic grid Reynolds number. Large Reynolds numbers indicate regions where solution may experience some grid noise due to lack of enough horizontal friction.



NAMELIST

&ocean_bih_friction_general_nml

bih_friction_on
Must be true to use this module.
[logical]
k_smag_iso
This is the dimensionless Smagorinsky coefficient used to set the scale of the Smagorinsky isotropic viscosity.
[real, units: dimensionless]
k_smag_aniso
This is the dimensionless Smagorinsky coefficient used to set the scale of the Smagorinsky anisotropic viscosity.
[real, units: dimensionless]
vel_micom_iso
Velocity scale that is used for computing the MICOM isotropic viscosity.
[real, units: m/sec]
vel_micom_aniso
Velocity scale that is used for computing the MICOM anisotropic viscosity.
[real, units: m/sec]
equatorial_zonal
Orient the anisotropic friction within a latitudinal band according to zonal direction.
[real]
equatorial_zonal_lat
Latitudinal band to use the zonal friction orientation.
[real]
eq_vel_micom_iso
Velocity scale that is used for computing the MICOM isotropic viscosity within a user specified equatorial band.
[real]
eq_vel_micom_aniso
Velocity scale that is used for computing the MICOM anisotropic viscosity within a user specified equatorial band.
[real]
eq_lat_micom
Equatorial latitude band (degrees) within which the MICOM viscosity is set according to eq_vel_micom_iso and eq_vel_micom_aniso.
[real]
bottom_5point
To alleviate problems with small partial cells, it is often necessary to reduce the operator to the traditional 5-point Laplacian at the ocean bottom. This logical implements this mixing. Velocity scale that is used for computing the MICOM viscosity for 5point Laplacian at the bottom.
[logical]


DATA SETS

None.


ERROR MESSAGES

None.


REFERENCES

  1. S.M. Griffies and R.W. Hallberg, Biharmonic friction with a Smagorinsky viscosity for use in large-scale eddy-permitting ocean models Monthly Weather Review vol 128 (2000) pages 2935--2946
  2. R. D. Smith and J. C. McWilliams, Anisotropic viscosity for ocean models Ocean Modelling submitted 2002


COMPILER SPECIFICS

None.


PRECOMPILER OPTIONS

None.


LOADER OPTIONS

None.


TEST PROGRAM

None.


KNOWN BUGS

None.


NOTES

The ocean model can generally run with both Laplacian and biharmonic friction enabled at the same time. Such has been found useful for some eddying ocean simulations.


FUTURE PLANS

None.


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