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Module ocean_frazil_mod

Contact:  Stephen Griffies ,  David Jackett
Reviewers: 
Change History: WebCVS Log

OVERVIEW

This module computes the heating of seawater due to frazil ice formation.

Frazil can generally form at any vertical level, although it is common for climate models to assume it is formed only at k=1. In this case, pressure is assumed to be atmospheric for purposes of computing the freezing temperature of seawater.

The freezing temperature of seawater is computed one of two possible ways:

(1) simple way uses a linear function of salinity and assumes zero (i.e. atmospheric) pressure,

tfreeze(deg C) = a1*salinity(psu) with a1 = -0.054

(2) accurate way uses a nonlinear function of salinity(psu) and gauge pressure(dbar), where gauge pressure=absolute pressure - 10.1325 dbar.

tfreeze (deg C) = tf_num/tf_den tf_num = a0 + s*(a1 + sqrt(s)*(a2 + sqrt(s)*a3)) + p*(a4 + p*(a5 + s*a6)) tf_dem = b0 + p*(b1 + p*b2) + s*s*sqrt(s)*b3

check value : fp_theta(35,200,'air-sat') = -2.076426227617581 deg C fp_theta(35,200,'air-free') = -2.074408175943127 deg C

This method results in a more accurate freezing temperature than the simpler approach. It is also important for ice-shelf modelling to include a pressure dependence when the shelf penetrates into the water column.


OTHER MODULES USED

       constants_mod
    diag_manager_mod
             fms_mod
             mpp_mod
   ocean_domains_mod
ocean_parameters_mod
  ocean_tpm_util_mod
     ocean_types_mod

PUBLIC INTERFACE

ocean_frazil_init:
compute_frazil_heating:

PUBLIC DATA

None.

PUBLIC ROUTINES

  1. ocean_frazil_init

    DESCRIPTION
    Initialization code for the frazil diagnostic tracer.


  2. compute_frazil_heating

    DESCRIPTION
    Compute ocean heating due to formation of frazil-ice (Joules/m^2)

    Note that "frazil_factor" accounts for possibly different time stepping used in ocean model and the sea ice model. With mom4 using a leap-frog, and the GFDL ocean model SIS using forward, then frazil_factor=0.5. If use recommended tendency=twolevel in mom4, then frazil_factor=1.0



NAMELIST

&ocean_frazil_nml

use_this_module
If true, then compute frazil heating.
[logical]
debug_this_module
For debugging this module
[logical]
frazil_factor
This factor accounts for possibly different time stepping used in the sea ice model relative to the ocean model. If sea-ice and ocean use same time stepping schemes, then frazil_factor=1.0. If sea-ice uses a twolevel scheme and ocean a threelevel leap-frog, then frazil_factor=0.5. Default is 1.0 since the GFDL sea ice model SIS uses a two-level time stepping scheme and mom4 defaults to a staggered two-level scheme.
[real, units: dimensionless]
freezing_temp_simple
To use the simplefied freezing point temperature of seawater, as used in mom4p0. This is the default, since it is the equation used in the GFDL ice model.
[logical]
freezing_temp_accurate
To use the accurate freezing point temperature of seawater, which is a nonlinear function of salinity and pressure. This equation is recommended for use with ice-shelf modelling.
[logical]
frazil_only_in_surface
For typical case where compute frazil heating only in the surface grid cell. Will assume the gauge pressure is zero in this case when computing freezing temperature.
[logical]

DATA SETS

None.

ERROR MESSAGES

None.

REFERENCES

  1. "Updated algorithms for density, potential temperature, conservative temperature and freezing temperature of seawater", Jackett, McDougall, Feistel, Wright, and Griffies Journal of Atmospheric and Oceanic Technology, in press 2005.

COMPILER SPECIFICS

None.

PRECOMPILER OPTIONS

None.

LOADER OPTIONS

None.

TEST PROGRAM

None.

KNOWN BUGS

None.

NOTES

None.

FUTURE PLANS

None.

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