MOM_verticalGrid.F90

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!> Provides a transparent vertical ocean grid type and supporting routines
module mom_verticalgrid
 
! This file is part of MOM6. See LICENSE.md for the license.
 
use mom_error_handler, only : mom_error, mom_mesg, fatal
use mom_file_parser, only : get_param, log_param, log_version, param_file_type
use mom_unit_scaling, only : unit_scale_type
 
implicit none ; private
 
#include <MOM_memory.h>
 
public verticalgridinit, verticalgridend
public setverticalgridaxes, fix_restart_scaling
public get_flux_units, get_thickness_units, get_tr_flux_units
 
! A note on unit descriptions in comments: MOM6 uses units that can be rescaled for dimensional
! consistency testing. These are noted in comments with units like Z, H, L, and T, along with
! their mks counterparts with notation like "a velocity [Z T-1 ~> m s-1]".  If the units
! vary with the Boussinesq approximation, the Boussinesq variant is given first.
 
!> Describes the vertical ocean grid, including unit conversion factors
type, public :: verticalgrid_type
 
  ! Commonly used parameters
  integer :: ke     !< The number of layers/levels in the vertical
  real :: max_depth !< The maximum depth of the ocean [Z ~> m].
  real :: mks_g_earth !< The gravitational acceleration in unscaled MKS units [m s-2].
  real :: g_earth   !< The gravitational acceleration [L2 Z-1 T-2 ~> m s-2].
  real :: rho0      !< The density used in the Boussinesq approximation or nominal
                    !! density used to convert depths into mass units [kg m-3].
 
  ! Vertical coordinate descriptions for diagnostics and I/O
  character(len=40) :: zaxisunits !< The units that vertical coordinates are written in
  character(len=40) :: zaxislongname !< Coordinate name to appear in files,
                                  !! e.g. "Target Potential Density" or "Height"
  real, allocatable, dimension(:) :: slayer !< Coordinate values of layer centers
  real, allocatable, dimension(:) :: sinterface !< Coordinate values on interfaces
  integer :: direction = 1 !< Direction defaults to 1, positive up.
 
  ! The following variables give information about the vertical grid.
  logical :: boussinesq !< If true, make the Boussinesq approximation.
  real :: angstrom_h    !< A one-Angstrom thickness in the model thickness units [H ~> m or kg m-2].
  real :: angstrom_z    !< A one-Angstrom thickness in the model depth units [Z ~> m].
  real :: angstrom_m    !< A one-Angstrom thickness [m].
  real :: h_subroundoff !< A thickness that is so small that it can be added to a thickness of
                        !! Angstrom or larger without changing it at the bit level [H ~> m or kg m-2].
                        !! If Angstrom is 0 or exceedingly small, this is negligible compared to 1e-17 m.
  real, allocatable, dimension(:) :: &
    g_prime, &          !< The reduced gravity at each interface [L2 Z-1 T-2 ~> m s-2].
    rlay                !< The target coordinate value (potential density) in each layer [R ~> kg m-3].
  integer :: nkml = 0   !< The number of layers at the top that should be treated
                        !! as parts of a homogeneous region.
  integer :: nk_rho_varies = 0 !< The number of layers at the top where the
                        !! density does not track any target density.
  real :: h_to_kg_m2    !< A constant that translates thicknesses from the units of thickness to kg m-2.
  real :: kg_m2_to_h    !< A constant that translates thicknesses from kg m-2 to the units of thickness.
  real :: m_to_h        !< A constant that translates distances in m to the units of thickness.
  real :: h_to_m        !< A constant that translates distances in the units of thickness to m.
  real :: h_to_pa       !< A constant that translates the units of thickness to pressure [Pa].
  real :: h_to_z        !< A constant that translates thickness units to the units of depth.
  real :: z_to_h        !< A constant that translates depth units to thickness units.
  real :: h_to_rz       !< A constant that translates thickness units to the units of mass per unit area.
  real :: rz_to_h       !< A constant that translates mass per unit area units to thickness units.
  real :: h_to_mks      !< A constant that translates thickness units to its
                        !! MKS unit (m or kg m-2) based on GV%Boussinesq
 
  real :: m_to_h_restart = 0.0 !< A copy of the m_to_H that is used in restart files.
end type verticalgrid_type
 
contains
 
!> Allocates and initializes the ocean model vertical grid structure.
subroutine verticalgridinit( param_file, GV, US )
  type(param_file_type),   intent(in) :: param_file !< Parameter file handle/type
  type(verticalgrid_type), pointer    :: gv         !< The container for vertical grid data
  type(unit_scale_type),   intent(in) :: us         !< A dimensional unit scaling type
  ! This routine initializes the verticalGrid_type structure (GV).
  ! All memory is allocated but not necessarily set to meaningful values until later.
 
  ! Local variables
  integer :: nk, h_power
  real    :: h_rescale_factor
  ! This include declares and sets the variable "version".
# include "version_variable.h"
  character(len=16) :: mdl = 'MOM_verticalGrid'
 
  if (associated(gv)) call mom_error(fatal, &
     'verticalGridInit: called with an associated GV pointer.')
  allocate(gv)
 
  ! Read all relevant parameters and write them to the model log.
  call log_version(param_file, mdl, version, &
                   "Parameters providing information about the vertical grid.")
  call get_param(param_file, mdl, "G_EARTH", gv%mks_g_Earth, &
                 "The gravitational acceleration of the Earth.", &
                 units="m s-2", default = 9.80)
  call get_param(param_file, mdl, "RHO_0", gv%Rho0, &
                 "The mean ocean density used with BOUSSINESQ true to "//&
                 "calculate accelerations and the mass for conservation "//&
                 "properties, or with BOUSSINSEQ false to convert some "//&
                 "parameters from vertical units of m to kg m-2.", &
                 units="kg m-3", default=1035.0, scale=us%kg_m3_to_R)
  call get_param(param_file, mdl, "BOUSSINESQ", gv%Boussinesq, &
                 "If true, make the Boussinesq approximation.", default=.true.)
  call get_param(param_file, mdl, "ANGSTROM", gv%Angstrom_m, &
                 "The minimum layer thickness, usually one-Angstrom.", &
                 units="m", default=1.0e-10)
  call get_param(param_file, mdl, "H_RESCALE_POWER", h_power, &
                 "An integer power of 2 that is used to rescale the model's "//&
                 "intenal units of thickness.  Valid values range from -300 to 300.", &
                 units="nondim", default=0, debuggingparam=.true.)
  if (abs(h_power) > 300) call mom_error(fatal, "verticalGridInit: "//&
                 "H_RESCALE_POWER is outside of the valid range of -300 to 300.")
  h_rescale_factor = 1.0
  if (h_power /= 0) h_rescale_factor = 2.0**h_power
  if (.not.gv%Boussinesq) then
    call get_param(param_file, mdl, "H_TO_KG_M2", gv%H_to_kg_m2,&
                 "A constant that translates thicknesses from the model's "//&
                 "internal units of thickness to kg m-2.", units="kg m-2 H-1", &
                 default=1.0)
    gv%H_to_kg_m2 = gv%H_to_kg_m2 * h_rescale_factor
  else
    call get_param(param_file, mdl, "H_TO_M", gv%H_to_m, &
                 "A constant that translates the model's internal "//&
                 "units of thickness into m.", units="m H-1", default=1.0)
    gv%H_to_m = gv%H_to_m * h_rescale_factor
  endif
  gv%g_Earth = us%m_to_L**2*us%Z_to_m*us%T_to_s**2 * gv%mks_g_Earth
#ifdef STATIC_MEMORY_
  ! Here NK_ is a macro, while nk is a variable.
  call get_param(param_file, mdl, "NK", nk, &
                 "The number of model layers.", units="nondim", &
                 static_value=nk_)
  if (nk /= nk_) call mom_error(fatal, "verticalGridInit: " // &
       "Mismatched number of layers NK_ between MOM_memory.h and param_file")
 
#else
  call get_param(param_file, mdl, "NK", nk, &
                 "The number of model layers.", units="nondim", fail_if_missing=.true.)
#endif
  gv%ke = nk
 
  if (gv%Boussinesq) then
    gv%H_to_kg_m2 = us%R_to_kg_m3*gv%Rho0 * gv%H_to_m
    gv%kg_m2_to_H = 1.0 / gv%H_to_kg_m2
    gv%m_to_H = 1.0 / gv%H_to_m
    gv%Angstrom_H = gv%m_to_H * gv%Angstrom_m
    gv%H_to_MKS = gv%H_to_m
  else
    gv%kg_m2_to_H = 1.0 / gv%H_to_kg_m2
    gv%m_to_H = us%R_to_kg_m3*gv%Rho0 * gv%kg_m2_to_H
    gv%H_to_m = gv%H_to_kg_m2 / (us%R_to_kg_m3*gv%Rho0)
    gv%Angstrom_H = gv%Angstrom_m*1000.0*gv%kg_m2_to_H
    gv%H_to_MKS = gv%H_to_kg_m2
  endif
  gv%H_subroundoff = 1e-20 * max(gv%Angstrom_H,gv%m_to_H*1e-17)
  gv%H_to_Pa = gv%mks_g_Earth * gv%H_to_kg_m2
 
  gv%H_to_Z = gv%H_to_m * us%m_to_Z
  gv%Z_to_H = us%Z_to_m * gv%m_to_H
  gv%Angstrom_Z = us%m_to_Z * gv%Angstrom_m
 
  gv%H_to_RZ = gv%H_to_kg_m2 * us%kg_m3_to_R * us%m_to_Z
  gv%RZ_to_H = gv%kg_m2_to_H * us%R_to_kg_m3 * us%Z_to_m
 
! Log derivative values.
  call log_param(param_file, mdl, "M to THICKNESS", gv%m_to_H*h_rescale_factor)
  call log_param(param_file, mdl, "M to THICKNESS rescaled by 2^-n", gv%m_to_H)
  call log_param(param_file, mdl, "THICKNESS to M rescaled by 2^n", gv%H_to_m)
 
  allocate( gv%sInterface(nk+1) )
  allocate( gv%sLayer(nk) )
  allocate( gv%g_prime(nk+1) ) ; gv%g_prime(:) = 0.0
  ! The extent of Rlay should be changed to nk?
  allocate( gv%Rlay(nk+1) )    ; gv%Rlay(:) = 0.0
 
end subroutine verticalgridinit
 
!> Set the scaling factors for restart files to the scaling factors for this run.
subroutine fix_restart_scaling(GV)
  type(verticalgrid_type), intent(inout) :: gv   !< The ocean's vertical grid structure
 
  gv%m_to_H_restart = gv%m_to_H
end subroutine fix_restart_scaling
 
!> Returns the model's thickness units, usually m or kg/m^2.
function get_thickness_units(GV)
  character(len=48)                   :: get_thickness_units !< The vertical thickness units
  type(verticalgrid_type), intent(in) :: gv   !< The ocean's vertical grid structure
  !   This subroutine returns the appropriate units for thicknesses,
  ! depending on whether the model is Boussinesq or not and the scaling for
  ! the vertical thickness.
 
  if (gv%Boussinesq) then
    get_thickness_units = "m"
  else
    get_thickness_units = "kg m-2"
  endif
end function get_thickness_units
 
!> Returns the model's thickness flux units, usually m^3/s or kg/s.
function get_flux_units(GV)
  character(len=48)                   :: get_flux_units !< The thickness flux units
  type(verticalgrid_type), intent(in) :: gv   !< The ocean's vertical grid structure
  !   This subroutine returns the appropriate units for thickness fluxes,
  ! depending on whether the model is Boussinesq or not and the scaling for
  ! the vertical thickness.
 
  if (gv%Boussinesq) then
    get_flux_units = "m3 s-1"
  else
    get_flux_units = "kg s-1"
  endif
end function get_flux_units
 
!> Returns the model's tracer flux units.
function get_tr_flux_units(GV, tr_units, tr_vol_conc_units, tr_mass_conc_units)
  character(len=48)                      :: get_tr_flux_units !< The model's flux units
                                                              !! for a tracer.
  type(verticalgrid_type),    intent(in) :: gv                !< The ocean's vertical
                                                              !! grid structure.
  character(len=*), optional, intent(in) :: tr_units          !< Units for a tracer, for example
                                                              !! Celsius or PSU.
  character(len=*), optional, intent(in) :: tr_vol_conc_units !< The concentration units per unit
                                                              !! volume, for example if the units are
                                                              !! umol m-3, tr_vol_conc_units would
                                                              !! be umol.
  character(len=*), optional, intent(in) :: tr_mass_conc_units !< The concentration units per unit
                                                              !! mass of sea water, for example if
                                                              !! the units are mol kg-1,
                                                              !! tr_vol_conc_units would be mol.
 
  !   This subroutine returns the appropriate units for thicknesses and fluxes,
  ! depending on whether the model is Boussinesq or not and the scaling for
  ! the vertical thickness.
  integer :: cnt
 
  cnt = 0
  if (present(tr_units)) cnt = cnt+1
  if (present(tr_vol_conc_units)) cnt = cnt+1
  if (present(tr_mass_conc_units)) cnt = cnt+1
 
  if (cnt == 0) call mom_error(fatal, "get_tr_flux_units: One of the three "//&
    "arguments tr_units, tr_vol_conc_units, or tr_mass_conc_units "//&
    "must be present.")
  if (cnt > 1) call mom_error(fatal, "get_tr_flux_units: Only one of "//&
    "tr_units, tr_vol_conc_units, and tr_mass_conc_units may be present.")
  if (present(tr_units)) then
    if (gv%Boussinesq) then
      get_tr_flux_units = trim(tr_units)//" m3 s-1"
    else
      get_tr_flux_units = trim(tr_units)//" kg s-1"
    endif
  endif
  if (present(tr_vol_conc_units)) then
    if (gv%Boussinesq) then
      get_tr_flux_units = trim(tr_vol_conc_units)//" s-1"
    else
      get_tr_flux_units = trim(tr_vol_conc_units)//" m-3 kg s-1"
    endif
  endif
  if (present(tr_mass_conc_units)) then
    if (gv%Boussinesq) then
      get_tr_flux_units = trim(tr_mass_conc_units)//" kg-1 m3 s-1"
    else
      get_tr_flux_units = trim(tr_mass_conc_units)//" s-1"
    endif
  endif
 
end function get_tr_flux_units
 
!> This sets the coordinate data for the "layer mode" of the isopycnal model.
subroutine setverticalgridaxes( Rlay, GV, scale )
  type(verticalgrid_type), intent(inout) :: gv   !< The container for vertical grid data
  real, dimension(GV%ke),  intent(in)    :: rlay !< The layer target density [R ~> kg m-3]
  real,                    intent(in)    :: scale !< A unit scaling factor for Rlay
  ! Local variables
  integer :: k, nk
 
  nk = gv%ke
 
  gv%zAxisLongName = 'Target Potential Density'
  gv%zAxisUnits = 'kg m-3'
  do k=1,nk ; gv%sLayer(k) = scale*rlay(k) ; enddo
  if (nk > 1) then
    gv%sInterface(1) = scale * (1.5*rlay(1) - 0.5*rlay(2))
    do k=2,nk ; gv%sInterface(k) = scale * 0.5*( rlay(k-1) + rlay(k) ) ; enddo
    gv%sInterface(nk+1) = scale * (1.5*rlay(nk) - 0.5*rlay(nk-1))
  else
    gv%sInterface(1) = 0.0 ; gv%sInterface(nk+1) = 2.0*scale*rlay(nk)
  endif
 
end subroutine setverticalgridaxes
 
!> Deallocates the model's vertical grid structure.
subroutine verticalgridend( GV )
  type(verticalgrid_type), pointer :: gv !< The ocean's vertical grid structure
 
  deallocate( gv%g_prime, gv%Rlay )
  deallocate( gv%sInterface , gv%sLayer )
  deallocate( gv )
 
end subroutine verticalgridend
 
end module mom_verticalgrid