Module ocean_density_mod
OVERVIEW
Compute density and related quantities.
This module computes the in-situ density and its partial derivatives with
respect to potential temperature and with respect to salinity.
Based on McDougall, Wright, Jackett, and Feistel (2002). This
equation of state is valid over the range:
0psu <= salinity <= 40 psu
-3C <= theta <= 40C
0dbar <= pressure <= 8000dbar
Input variables are the following:
salinity in psu
potential temperature (theta) in deg C
pressure in dbars (1bar = 10dbar = 10^5 Newton/m^2 = 10^5 Pascals).
Note that in the ocean, pressure increases roughly by 1dbar for each meter depth.
Also note that pressure is the "gauge" pressure, which is the absolute pressure
minus the pressure of a standard atmosphere, which is 10.1325 dbars.
check values (kindly provided by David Jackett)
rho(s=20psu,theta=20C,p=1000dbar) = 1017.72674313979 (kg/m^3)
alpha(s=20psu,theta=20C,p=1000dbar) = 2.524181985549684e-4 (1/C)
beta(s=20psu,theta=20C,p=1000dbar) = 7.382804621244401e-4 (1/psu)
This equation of state should be suitable for all purposes of realistic
ocean climate modeling.
B. Linear equation for use in idealized Boussinesq studies
This equation renders density a linear function of potential
temperature. All nonlinearities are ignored, as are salinity and
pressure effects. Since there are no compressibility effects in
this equations of state, it is only appropriate for Boussinesq
studies.
The valid range for T and S is arbitrary for linearized density.
However the range is restricted to the range for the standard EOS
to keep density gradients within reasonable limits.
So valid ranges are restricted to s=0 to 50 psu, t=-10 to 50 deg C
OTHER MODULES USED
constants_mod
diag_manager_mod
fms_mod
mpp_domains_mod
mpp_mod
platform_mod
time_manager_mod
ocean_domains_mod
ocean_operators_mod
ocean_pressure_mod
ocean_types_mod
ocean_util_mod
ocean_workspace_mod
PUBLIC INTERFACE
PUBLIC DATA
None.
PUBLIC ROUTINES
-
ocean_density_init
-
DESCRIPTION
- Initialize the density module
-
update_ocean_density
-
DESCRIPTION
- Compute ocean density and related fields.
-
update_ocean_density_taup1
-
DESCRIPTION
- Compute ocean density at taup1
-
density_field
-
DESCRIPTION
- Compute density for all grid points.
Note that pressure here is
gauge pressure = absolute pressure - press_standard
and salinity is in model units (psu).
-
density_level
-
DESCRIPTION
- Compute density at a particular k-level. Note that pressure here is
the gauge pressure = absolute pressure - press_standard
-
density_line
-
DESCRIPTION
- Compute density at a particular k-level and j index. This scheme
is used in the vectorized version of the full convection scheme.
Note that pressure here is the
gauge pressure = absolute pressure - press_standard
-
potential_density
-
DESCRIPTION
- Compute potential density referenced to some given gauge pressure.
Note that potential density referenced to the surface (i.e., sigma_0)
has a zero gauge pressure, so pressure=0.0 should be the argument
to the function.
-
density_sfc
-
DESCRIPTION
- Compute density as a function of surface salinity,
surface theta, and insitu gauge pressure.
For use in KPP mixed layer scheme
-
density_point
-
DESCRIPTION
- Compute density at a single model grid point. Note that pressure here
is the gauge pressure = absolute pressure - press_standard
-
density_derivs_field
-
DESCRIPTION
- Compute partial derivative of density with respect to potential
temperature and with respect to salinity. Hold pressure constant.
Pressure here is gauge pressure = absolute press - press_standard
-
density_derivs_point
-
DESCRIPTION
- Compute partial derivative of density with respect to potential
temperature and with respect to salinity. Do so here for a point.
Pressure here is gauge pressure = absolute pressure - press_standard
-
density_delta_z
-
DESCRIPTION
- rho(k)-rho(k+1) for all i,j with both temperatures referenced to the
deeper pressure depth. Of use for KPP scheme.
-
density_delta_sfc
-
DESCRIPTION
- rho(1)-rho(k+1) for all i,j. Of use for KPP scheme.
-
ocean_density_end
-
DESCRIPTION
- Write density field to a restart.
-
ocean_density_chksum
-
DESCRIPTION
- Compute checksums for density.
NAMELIST
&ocean_density_nml
-
s_test
Salinity for testing the EOS.
[real, units: psu]
-
press_standard
Standard atmospheric pressure (dbar). The realistic
EOS used in mom4 requires gauge pressuer as an argument
rather than absolute pressure. Gauge pressure is
absolute pressure minus a standard atmospheric pressure
of 10.1325dbar.
For models that do have a realistic atmospheric loading, then it
is appropriate to remove 10.1325dbar prior to computing the EOS.
For those cases with zero atmospheric pressure, then it is not
necessary to remove the standard atmosphere. As most model are
presently run with zero atmospheric pressure, the default for the
press_standard is 0.0.
[real, units: dbar]
-
t_test
Potential temperature for testing the EOS.
[real, units: C]
-
p_test
Gauge pressure for testing the EOS.
[real, units: dbar]
-
linear_eos
Set to true if wish to use the linear equation of state.
[logical]
-
alpha_linear_eos
Constant "thermal expansion coefficient" for EOS
rho = rho0 - alpha_linear_eos*theta + beta_linear_eos*salinity
[real]
-
beta_linear_eos
Constant "saline contraction coefficient" for EOS
rho = rho0 - alpha_linear_eos*theta + beta_linear_eos*salinity
[real]
-
potrho_press
Gauge pressure for computing diagnostic potential density
[real, units: dbar]
-
potrho_min
Minimum potential density used to partition vertical according to potential density.
[real, units: kg/m^3]
-
potrho_max
Maximum potential density used to partition vertical according to potential density.
[real, units: kg/m^3]
-
theta_min
Minimum potential temperature used to partition vertical according to theta.
[real, units: C]
-
theta_max
Maximum potential temperature used to partition vertical according to theta.
[real, units: C]
-
layer_nk
Number of classes used to partition vertical according to potential density
or potential temperature. Used for diagnostics.
[integer]
-
debug_density
For debugging nonlinear equation of state
[logical]
DATA SETS
None.
ERROR MESSAGES
None.
REFERENCES
- Feistel (2003)
A new extended Gibbs thermodynamic potential of seawater
Progress in Oceanography. vol 58, pages 43-114.
- McDougall, Jackett, Wright, and Feistel (2002)
Accurate and computationally efficient algorithms for
potential temperatue and density of seawater
Journal of Atmospheric and Oceanic Technology, submitted 2002
- Jackett, McDougall, Feistel, Wright, and Griffies (2004)
Updated algorithms for density, potential temperature,
conservative temperature, and freezing temperature of
seawater.
Journal of Atmospheric and Oceanic Technology, 2004 submitted
- S.M. Griffies, M.J. Harrison, R.C. Pacanowski, and A. Rosati
A Technical Guide to MOM4 (2003)
- S.M. Griffies, R.C. Pacanowski, R.M. Schmidt, and V. Balaji
Tracer Conservation with an Explicit Free Surface Method for
Z-coordinate Ocean Models
Monthly Weather Review (2001) vol 129 pages 1081--1098
COMPILER SPECIFICS
None.
PRECOMPILER OPTIONS
None.
LOADER OPTIONS
None.
TEST PROGRAM
None.
KNOWN BUGS
None.
NOTES
Density is computed as a function of potential temperature (C), salinity (psu),
and in-situ pressure (dbar). The pressure contribution includes that from
the free surface height and the atmospheric pressure. Because the baroclinic
component of the hydrostatic pressure is not known until the density is known,
the baroclinic pressure contribution to density is lagged by a single time step.
rho(tau) = rho[theta(tau),s(tau), p_atm(tau) + p_fs(tau) + p_baroclinic(tau-1)]
FUTURE PLANS
None.