oil_tracer.F90

!> A tracer package to mimic dissolved oil.
module oil_tracer

! This file is part of MOM6. See LICENSE.md for the license.

use mom_diag_mediator, only : diag_ctrl
use mom_error_handler, only : mom_error, fatal, warning
use mom_file_parser, only : get_param, log_param, log_version, param_file_type
use mom_forcing_type, only : forcing
use mom_grid, only : ocean_grid_type
use mom_hor_index, only : hor_index_type
use mom_io, only : file_exists, mom_read_data, slasher, vardesc, var_desc, query_vardesc
use mom_open_boundary, only : ocean_obc_type
use mom_restart, only : query_initialized, mom_restart_cs
use mom_sponge, only : set_up_sponge_field, sponge_cs
use mom_time_manager, only : time_type, time_type_to_real
use mom_tracer_registry, only : register_tracer, tracer_registry_type
use mom_tracer_diabatic, only : tracer_vertdiff, applytracerboundaryfluxesinout
use mom_tracer_z_init, only : tracer_z_init
use mom_unit_scaling, only : unit_scale_type
use mom_variables, only : surface, thermo_var_ptrs
use mom_verticalgrid, only : verticalgrid_type

use coupler_types_mod, only : coupler_type_set_data, ind_csurf
use atmos_ocean_fluxes_mod, only : aof_set_coupler_flux

implicit none ; private

#include <MOM_memory.h>

public register_oil_tracer, initialize_oil_tracer
public oil_tracer_column_physics, oil_tracer_surface_state
public oil_stock, oil_tracer_end

integer, parameter :: ntr_max = 20 !< the maximum number of tracers in this module.

!> The control structure for the oil tracer package
type, public :: oil_tracer_cs ; private
  integer :: ntr    !< The number of tracers that are actually used.
  logical :: coupled_tracers = .false. !< These tracers are not offered to the coupler.
  character(len=200) :: ic_file !< The file in which the age-tracer initial values
                                !! can be found, or an empty string for internal initialization.
  logical :: z_ic_file !< If true, the IC_file is in Z-space.  The default is false.
  real :: oil_source_longitude !< Latitude of source location (geographic)
  real :: oil_source_latitude  !< Longitude of source location (geographic)
  integer :: oil_source_i=-999 !< Local i of source location (computational)
  integer :: oil_source_j=-999 !< Local j of source location (computational)
  real :: oil_source_rate     !< Rate of oil injection [kg T-1 ~> kg s-1]
  real :: oil_start_year      !< The year in which tracers start aging, or at which the
                              !! surface value equals young_val, in years.
  real :: oil_end_year        !< The year in which tracers start aging, or at which the
                              !! surface value equals young_val, in years.
  type(time_type), pointer :: time => null() !< A pointer to the ocean model's clock.
  type(tracer_registry_type), pointer :: tr_reg => null() !< A pointer to the MOM tracer registry
  real, pointer :: tr(:,:,:,:) => null() !< The array of tracers used in this subroutine, in g m-3?
  real, dimension(NTR_MAX) :: ic_val = 0.0    !< The (uniform) initial condition value.
  real, dimension(NTR_MAX) :: young_val = 0.0 !< The value assigned to tr at the surface.
  real, dimension(NTR_MAX) :: land_val = -1.0 !< The value of tr used where land is masked out.
  real, dimension(NTR_MAX) :: sfc_growth_rate !< The exponential growth rate for the surface value [year-1].
  real, dimension(NTR_MAX) :: oil_decay_days  !< Decay time scale of oil [days]
  real, dimension(NTR_MAX) :: oil_decay_rate  !< Decay rate of oil [T-1 ~> s-1] calculated from oil_decay_days
  integer, dimension(NTR_MAX) :: oil_source_k !< Layer of source
  logical :: oil_may_reinit  !< If true, oil tracers may be reset by the initialization code
                             !! if they are not found in the restart files.
  integer, dimension(NTR_MAX) :: ind_tr !< Indices returned by aof_set_coupler_flux if it is used and the
                                        !! surface tracer concentrations are to be provided to the coupler.
  type(vardesc) :: tr_desc(ntr_max) !< Descriptions and metadata for the tracers

  type(diag_ctrl), pointer :: diag => null() !< A structure that is used to
                                   !! regulate the timing of diagnostic output.
  type(mom_restart_cs), pointer :: restart_csp => null() !< A pointer to the restart control structure
end type oil_tracer_cs

contains

!> Register oil tracer fields and subroutines to be used with MOM.
function register_oil_tracer(HI, GV, US, param_file, CS, tr_Reg, restart_CS)
  type(hor_index_type),       intent(in) :: HI   !< A horizontal index type structure
  type(verticalgrid_type),    intent(in) :: GV   !< The ocean's vertical grid structure
  type(unit_scale_type),      intent(in) :: US   !< A dimensional unit scaling type
  type(param_file_type),      intent(in) :: param_file !< A structure to parse for run-time parameters
  type(oil_tracer_cs),        pointer    :: CS   !< A pointer that is set to point to the control
                                                 !! structure for this module
  type(tracer_registry_type), pointer    :: tr_Reg !< A pointer that is set to point to the control
                                                 !! structure for the tracer advection and
                                                 !! diffusion module
  type(mom_restart_cs),       pointer    :: restart_CS !< A pointer to the restart control structure

  ! Local variables
  character(len=40)  :: mdl = "oil_tracer" ! This module's name.
! This include declares and sets the variable "version".
#include "version_variable.h"
  character(len=200) :: inputdir ! The directory where the input files are.
  character(len=48)  :: var_name ! The variable's name.
  character(len=3)   :: name_tag ! String for creating identifying oils
  character(len=48) :: flux_units ! The units for tracer fluxes, here
                            ! kg(oil) s-1 or kg(oil) m-3 kg(water) s-1.
  real, pointer :: tr_ptr(:,:,:) => null()
  logical :: register_oil_tracer
  integer :: isd, ied, jsd, jed, nz, m, i, j
  isd = hi%isd ; ied = hi%ied ; jsd = hi%jsd ; jed = hi%jed ; nz = gv%ke

  if (associated(cs)) then
    call mom_error(warning, "register_oil_tracer called with an "// &
                             "associated control structure.")
    return
  endif
  allocate(cs)

  ! Read all relevant parameters and write them to the model log.
  call log_version(param_file, mdl, version, "")
  call get_param(param_file, mdl, "OIL_IC_FILE", cs%IC_file, &
                 "The file in which the oil tracer initial values can be "//&
                 "found, or an empty string for internal initialization.", &
                 default=" ")
  if ((len_trim(cs%IC_file) > 0) .and. (scan(cs%IC_file,'/') == 0)) then
    ! Add the directory if CS%IC_file is not already a complete path.
    call get_param(param_file, mdl, "INPUTDIR", inputdir, default=".")
    cs%IC_file = trim(slasher(inputdir))//trim(cs%IC_file)
    call log_param(param_file, mdl, "INPUTDIR/CFC_IC_FILE", cs%IC_file)
  endif
  call get_param(param_file, mdl, "OIL_IC_FILE_IS_Z", cs%Z_IC_file, &
                 "If true, OIL_IC_FILE is in depth space, not layer space", &
                 default=.false.)

  call get_param(param_file, mdl, "OIL_MAY_REINIT", cs%oil_may_reinit, &
                 "If true, oil tracers may go through the initialization "//&
                 "code if they are not found in the restart files. "//&
                 "Otherwise it is a fatal error if the oil tracers are not "//&
                 "found in the restart files of a restarted run.", &
                 default=.false.)
  call get_param(param_file, mdl, "OIL_SOURCE_LONGITUDE", cs%oil_source_longitude, &
                 "The geographic longitude of the oil source.", units="degrees E", &
                 fail_if_missing=.true.)
  call get_param(param_file, mdl, "OIL_SOURCE_LATITUDE", cs%oil_source_latitude, &
                 "The geographic latitude of the oil source.", units="degrees N", &
                 fail_if_missing=.true.)
  call get_param(param_file, mdl, "OIL_SOURCE_LAYER", cs%oil_source_k, &
                 "The layer into which the oil is introduced, or a "//&
                 "negative number for a vertically uniform source, "//&
                 "or 0 not to use this tracer.", units="Layer", default=0)
  call get_param(param_file, mdl, "OIL_SOURCE_RATE", cs%oil_source_rate, &
                 "The rate of oil injection.", units="kg s-1", scale=us%T_to_s, default=1.0)
  call get_param(param_file, mdl, "OIL_DECAY_DAYS", cs%oil_decay_days, &
                 "The decay timescale in days (if positive), or no decay "//&
                 "if 0, or use the temperature dependent decay rate of "//&
                 "Adcroft et al. (GRL, 2010) if negative.", units="days", &
                 default=0.0)
  call get_param(param_file, mdl, "OIL_DATED_START_YEAR", cs%oil_start_year, &
                 "The time at which the oil source starts", units="years", &
                 default=0.0)
  call get_param(param_file, mdl, "OIL_DATED_END_YEAR", cs%oil_end_year, &
                 "The time at which the oil source ends", units="years", &
                 default=1.0e99)

  cs%ntr = 0
  cs%oil_decay_rate(:) = 0.
  do m=1,ntr_max
    if (cs%oil_source_k(m)/=0) then
      write(name_tag(1:3),'("_",I2.2)') m
      cs%ntr = cs%ntr + 1
      cs%tr_desc(m) = var_desc("oil"//trim(name_tag), "kg m-3", "Oil Tracer", caller=mdl)
      cs%IC_val(m) = 0.0
      if (cs%oil_decay_days(m)>0.) then
        cs%oil_decay_rate(m) = 1. / (86400.0*us%s_to_T * cs%oil_decay_days(m))
      elseif (cs%oil_decay_days(m)<0.) then
        cs%oil_decay_rate(m) = -1.
      endif
    endif
  enddo
  call log_param(param_file, mdl, "OIL_DECAY_RATE", us%s_to_T*cs%oil_decay_rate(1:cs%ntr))

  ! This needs to be changed if the units of tracer are changed above.
  if (gv%Boussinesq) then ; flux_units = "kg s-1"
  else ; flux_units = "kg m-3 kg s-1" ; endif

  allocate(cs%tr(isd:ied,jsd:jed,nz,cs%ntr)) ; cs%tr(:,:,:,:) = 0.0

  do m=1,cs%ntr
    ! This is needed to force the compiler not to do a copy in the registration
    ! calls.  Curses on the designers and implementers of Fortran90.
    tr_ptr => cs%tr(:,:,:,m)
    call query_vardesc(cs%tr_desc(m), name=var_name, caller="register_oil_tracer")
    ! Register the tracer for horizontal advection, diffusion, and restarts.
    call register_tracer(tr_ptr, tr_reg, param_file, hi, gv, tr_desc=cs%tr_desc(m), &
                         registry_diags=.true., flux_units=flux_units, restart_cs=restart_cs, &
                         mandatory=.not.cs%oil_may_reinit)

    !   Set coupled_tracers to be true (hard-coded above) to provide the surface
    ! values to the coupler (if any).  This is meta-code and its arguments will
    ! currently (deliberately) give fatal errors if it is used.
    if (cs%coupled_tracers) &
      cs%ind_tr(m) = aof_set_coupler_flux(trim(var_name)//'_flux', &
          flux_type=' ', implementation=' ', caller="register_oil_tracer")
  enddo

  cs%tr_Reg => tr_reg
  cs%restart_CSp => restart_cs
  register_oil_tracer = .true.

end function register_oil_tracer

!> Initialize the oil tracers and set up tracer output
subroutine initialize_oil_tracer(restart, day, G, GV, US, h, diag, OBC, CS, &
                                  sponge_CSp)
  logical,                            intent(in) :: restart !< .true. if the fields have already
                                                         !! been read from a restart file.
  type(time_type),            target, intent(in) :: day  !< Time of the start of the run.
  type(ocean_grid_type),              intent(in) :: G    !< The ocean's grid structure
  type(verticalgrid_type),            intent(in) :: GV   !< The ocean's vertical grid structure
  type(unit_scale_type),              intent(in) :: US   !< A dimensional unit scaling type
  real, dimension(SZI_(G),SZJ_(G),SZK_(G)), &
                                      intent(in) :: h    !< Layer thicknesses [H ~> m or kg m-2]
  type(diag_ctrl),            target, intent(in) :: diag !< A structure that is used to regulate
                                                         !! diagnostic output.
  type(ocean_obc_type),               pointer    :: OBC  !< This open boundary condition type specifies
                                                         !! whether, where, and what open boundary
                                                         !! conditions are used.
  type(oil_tracer_cs),                pointer    :: CS !< The control structure returned by a previous
                                                       !! call to register_oil_tracer.
  type(sponge_cs),                    pointer    :: sponge_CSp !< Pointer to the control structure for the sponges.

  ! Local variables
  character(len=16) :: name     ! A variable's name in a NetCDF file.
  character(len=72) :: longname ! The long name of that variable.
  character(len=48) :: units    ! The dimensions of the variable.
  character(len=48) :: flux_units ! The units for age tracer fluxes, either
                                ! years m3 s-1 or years kg s-1.
  logical :: OK
  integer :: i, j, k, is, ie, js, je, isd, ied, jsd, jed, nz, m
  integer :: IsdB, IedB, JsdB, JedB

  if (.not.associated(cs)) return
  if (cs%ntr < 1) return
  is = g%isc ; ie = g%iec ; js = g%jsc ; je = g%jec ; nz = gv%ke
  isd = g%isd ; ied = g%ied ; jsd = g%jsd ; jed = g%jed
  isdb = g%IsdB ; iedb = g%IedB ; jsdb = g%JsdB ; jedb = g%JedB

  ! Establish location of source
  do j=g%jsdB+1,g%jed ; do i=g%isdB+1,g%ied
    ! This test for i,j index is specific to a lat/lon (non-rotated grid).
    ! and needs to be generalized to work properly on the tri-polar grid.
    if (cs%oil_source_longitude<g%geoLonBu(i,j) .and. &
        cs%oil_source_longitude>=g%geoLonBu(i-1,j) .and. &
        cs%oil_source_latitude<g%geoLatBu(i,j) .and. &
        cs%oil_source_latitude>=g%geoLatBu(i,j-1) ) then
      cs%oil_source_i=i
      cs%oil_source_j=j
    endif
  enddo ; enddo

  cs%Time => day
  cs%diag => diag

  do m=1,cs%ntr
    call query_vardesc(cs%tr_desc(m), name=name, caller="initialize_oil_tracer")
    if ((.not.restart) .or. (cs%oil_may_reinit .and. .not. &
        query_initialized(cs%tr(:,:,:,m), name, cs%restart_CSp))) then

      if (len_trim(cs%IC_file) > 0) then
  !  Read the tracer concentrations from a netcdf file.
        if (.not.file_exists(cs%IC_file, g%Domain)) &
          call mom_error(fatal, "initialize_oil_tracer: "// &
                                 "Unable to open "//cs%IC_file)

        if (cs%Z_IC_file) then
          ok = tracer_z_init(cs%tr(:,:,:,m), h, cs%IC_file, name, &
                             g, us, -1e34, 0.0) ! CS%land_val(m))
          if (.not.ok) then
            ok = tracer_z_init(cs%tr(:,:,:,m), h, cs%IC_file, &
                     trim(name), g, us, -1e34, 0.0) ! CS%land_val(m))
            if (.not.ok) call mom_error(fatal,"initialize_oil_tracer: "//&
                    "Unable to read "//trim(name)//" from "//&
                    trim(cs%IC_file)//".")
          endif
        else
          call mom_read_data(cs%IC_file, trim(name), cs%tr(:,:,:,m), g%Domain)
        endif
      else
        do k=1,nz ; do j=js,je ; do i=is,ie
          if (g%mask2dT(i,j) < 0.5) then
            cs%tr(i,j,k,m) = cs%land_val(m)
          else
            cs%tr(i,j,k,m) = cs%IC_val(m)
          endif
        enddo ; enddo ; enddo
      endif

    endif ! restart
  enddo ! Tracer loop

  if (associated(obc)) then
  ! Put something here...
  endif

end subroutine initialize_oil_tracer

!> Apply sources, sinks, diapycnal mixing and rising motions to the oil tracers
subroutine oil_tracer_column_physics(h_old, h_new, ea, eb, fluxes, dt, G, GV, US, CS, tv, &
              evap_CFL_limit, minimum_forcing_depth)
  type(ocean_grid_type),   intent(in) :: G    !< The ocean's grid structure
  type(verticalgrid_type), intent(in) :: GV   !< The ocean's vertical grid structure
  real, dimension(SZI_(G),SZJ_(G),SZK_(G)), &
                           intent(in) :: h_old !< Layer thickness before entrainment [H ~> m or kg m-2].
  real, dimension(SZI_(G),SZJ_(G),SZK_(G)), &
                           intent(in) :: h_new !< Layer thickness after entrainment [H ~> m or kg m-2].
  real, dimension(SZI_(G),SZJ_(G),SZK_(G)), &
                           intent(in) :: ea   !< an array to which the amount of fluid entrained
                                              !! from the layer above during this call will be
                                              !! added [H ~> m or kg m-2].
  real, dimension(SZI_(G),SZJ_(G),SZK_(G)), &
                           intent(in) :: eb   !< an array to which the amount of fluid entrained
                                              !! from the layer below during this call will be
                                              !! added [H ~> m or kg m-2].
  type(forcing),           intent(in) :: fluxes !< A structure containing pointers to thermodynamic
                                              !! and tracer forcing fields.  Unused fields have NULL ptrs.
  real,                    intent(in) :: dt   !< The amount of time covered by this call [T ~> s]
  type(unit_scale_type),   intent(in) :: US   !< A dimensional unit scaling type
  type(oil_tracer_cs),     pointer    :: CS   !< The control structure returned by a previous
                                              !! call to register_oil_tracer.
  type(thermo_var_ptrs),   intent(in) :: tv   !< A structure pointing to various thermodynamic variables
  real,          optional, intent(in) :: evap_CFL_limit !< Limit on the fraction of the water that can
                                              !! be fluxed out of the top layer in a timestep [nondim]
  real,          optional, intent(in) :: minimum_forcing_depth !< The smallest depth over which
                                              !! fluxes can be applied [H ~> m or kg m-2]
!   This subroutine applies diapycnal diffusion and any other column
! tracer physics or chemistry to the tracers from this file.
! This is a simple example of a set of advected passive tracers.

! The arguments to this subroutine are redundant in that
!     h_new(k) = h_old(k) + ea(k) - eb(k-1) + eb(k) - ea(k+1)

  ! Local variables
  real, dimension(SZI_(G),SZJ_(G),SZK_(G)) :: h_work ! Used so that h can be modified
  real :: Isecs_per_year = 1.0 / (365.0*86400.0)
  real :: year, h_total, ldecay
  integer :: i, j, k, is, ie, js, je, nz, m, k_max
  is = g%isc ; ie = g%iec ; js = g%jsc ; je = g%jec ; nz = gv%ke

  if (.not.associated(cs)) return
  if (cs%ntr < 1) return

  if (present(evap_cfl_limit) .and. present(minimum_forcing_depth)) then
    do m=1,cs%ntr
      do k=1,nz ;do j=js,je ; do i=is,ie
        h_work(i,j,k) = h_old(i,j,k)
      enddo ; enddo ; enddo
      call applytracerboundaryfluxesinout(g, gv, cs%tr(:,:,:,m), dt, fluxes, h_work, &
                                          evap_cfl_limit, minimum_forcing_depth)
      call tracer_vertdiff(h_work, ea, eb, dt, cs%tr(:,:,:,m), g, gv)
    enddo
  else
    do m=1,cs%ntr
      call tracer_vertdiff(h_old, ea, eb, dt, cs%tr(:,:,:,m), g, gv)
    enddo
  endif

  year = time_type_to_real(cs%Time) * isecs_per_year

  ! Decay tracer (limit decay rate to 1/dt - just in case)
  do m=2,cs%ntr
    do k=1,nz ; do j=js,je ; do i=is,ie
      !CS%tr(i,j,k,m) = CS%tr(i,j,k,m) - dt*CS%oil_decay_rate(m)*CS%tr(i,j,k,m) ! Simple
      !CS%tr(i,j,k,m) = CS%tr(i,j,k,m) - min(dt*CS%oil_decay_rate(m),1.)*CS%tr(i,j,k,m) ! Safer
      if (cs%oil_decay_rate(m)>0.) then
        cs%tr(i,j,k,m) = g%mask2dT(i,j)*max(1. - dt*cs%oil_decay_rate(m),0.)*cs%tr(i,j,k,m) ! Safest
      elseif (cs%oil_decay_rate(m)<0.) then
        ldecay = 12.*(3.0**(-(tv%T(i,j,k)-20.)/10.)) ! Timescale [days]
        ldecay = 1. / (86400.*us%s_to_T * ldecay) ! Rate [T-1 ~> s-1]
        cs%tr(i,j,k,m) = g%mask2dT(i,j)*max(1. - dt*ldecay,0.)*cs%tr(i,j,k,m)
      endif
    enddo ; enddo ; enddo
  enddo

  ! Add oil at the source location
  if (year>=cs%oil_start_year .and. year<=cs%oil_end_year .and. &
      cs%oil_source_i>-999 .and. cs%oil_source_j>-999) then
    i=cs%oil_source_i ; j=cs%oil_source_j
    k_max=nz ; h_total=0.
    do k=nz, 2, -1
      h_total = h_total + h_new(i,j,k)
      if (h_total<10.) k_max=k-1 ! Find bottom most interface that is 10 m above bottom
    enddo
    do m=1,cs%ntr
      k=cs%oil_source_k(m)
      if (k>0) then
        k=min(k,k_max) ! Only insert k or first layer with interface 10 m above bottom
        cs%tr(i,j,k,m) = cs%tr(i,j,k,m) + cs%oil_source_rate*dt / &
                ((h_new(i,j,k)+gv%H_subroundoff) * g%US%L_to_m**2*g%areaT(i,j) )
      elseif (k<0) then
        h_total=gv%H_subroundoff
        do k=1, nz
          h_total = h_total + h_new(i,j,k)
        enddo
        do k=1, nz
          cs%tr(i,j,k,m) = cs%tr(i,j,k,m) + cs%oil_source_rate*dt/(h_total &
                                           * g%US%L_to_m**2*g%areaT(i,j) )
        enddo
      endif
    enddo
  endif

end subroutine oil_tracer_column_physics

!> Calculate the mass-weighted integral of the oil tracer stocks, returning the number of stocks it
!! has calculated.  If the stock_index is present, only the stock corresponding to that coded index is returned.
function oil_stock(h, stocks, G, GV, CS, names, units, stock_index)
  type(ocean_grid_type),              intent(in)    :: G    !< The ocean's grid structure
  type(verticalgrid_type),            intent(in)    :: GV   !< The ocean's vertical grid structure
  real, dimension(SZI_(G),SZJ_(G),SZK_(G)), intent(in) :: h    !< Layer thicknesses [H ~> m or kg m-2]
  real, dimension(:),                 intent(out)   :: stocks !< the mass-weighted integrated amount of each
                                                              !! tracer, in kg times concentration units [kg conc].
  type(oil_tracer_cs),                pointer       :: CS   !< The control structure returned by a previous
                                                            !! call to register_oil_tracer.
  character(len=*), dimension(:),     intent(out)   :: names  !< the names of the stocks calculated.
  character(len=*), dimension(:),     intent(out)   :: units  !< the units of the stocks calculated.
  integer, optional,                  intent(in)    :: stock_index !< the coded index of a specific stock
                                                                   !! being sought.
  integer                                           :: oil_stock !< The number of stocks calculated here.

! This function calculates the mass-weighted integral of all tracer stocks,
! returning the number of stocks it has calculated.  If the stock_index
! is present, only the stock corresponding to that coded index is returned.

  ! Local variables
  integer :: i, j, k, is, ie, js, je, nz, m
  is = g%isc ; ie = g%iec ; js = g%jsc ; je = g%jec ; nz = gv%ke

  oil_stock = 0
  if (.not.associated(cs)) return
  if (cs%ntr < 1) return

  if (present(stock_index)) then ; if (stock_index > 0) then
    ! Check whether this stock is available from this routine.

    ! No stocks from this routine are being checked yet.  Return 0.
    return
  endif ; endif

  do m=1,cs%ntr
    call query_vardesc(cs%tr_desc(m), name=names(m), units=units(m), caller="oil_stock")
    units(m) = trim(units(m))//" kg"
    stocks(m) = 0.0
    do k=1,nz ; do j=js,je ; do i=is,ie
      stocks(m) = stocks(m) + cs%tr(i,j,k,m) * &
                             (g%mask2dT(i,j) * g%US%L_to_m**2*g%areaT(i,j) * h(i,j,k))
    enddo ; enddo ; enddo
    stocks(m) = gv%H_to_kg_m2 * stocks(m)
  enddo
  oil_stock = cs%ntr

end function oil_stock

!> This subroutine extracts the surface fields from this tracer package that
!! are to be shared with the atmosphere in coupled configurations.
!! This particular tracer package does not report anything back to the coupler.
subroutine oil_tracer_surface_state(sfc_state, h, G, CS)
  type(ocean_grid_type),  intent(in)    :: G  !< The ocean's grid structure.
  type(surface),          intent(inout) :: sfc_state !< A structure containing fields that
                                              !! describe the surface state of the ocean.
  real, dimension(SZI_(G),SZJ_(G),SZK_(G)), &
                          intent(in)    :: h  !< Layer thickness [H ~> m or kg m-2].
  type(oil_tracer_cs),    pointer       :: CS !< The control structure returned by a previous
                                              !! call to register_oil_tracer.

  ! This particular tracer package does not report anything back to the coupler.
  ! The code that is here is just a rough guide for packages that would.

  integer :: m, is, ie, js, je, isd, ied, jsd, jed
  is = g%isc ; ie = g%iec ; js = g%jsc ; je = g%jec
  isd = g%isd ; ied = g%ied ; jsd = g%jsd ; jed = g%jed

  if (.not.associated(cs)) return

  if (cs%coupled_tracers) then
    do m=1,cs%ntr
      !   This call loads the surface values into the appropriate array in the
      ! coupler-type structure.
      call coupler_type_set_data(cs%tr(:,:,1,m), cs%ind_tr(m), ind_csurf, &
                   sfc_state%tr_fields, idim=(/isd, is, ie, ied/), &
                   jdim=(/jsd, js, je, jed/) )
    enddo
  endif

end subroutine oil_tracer_surface_state

!> Deallocate memory associated with this tracer package
subroutine oil_tracer_end(CS)
  type(oil_tracer_cs), pointer :: CS !< The control structure returned by a previous
                                     !! call to register_oil_tracer.
  integer :: m

  if (associated(cs)) then
    if (associated(cs%tr)) deallocate(cs%tr)
    deallocate(cs)
  endif
end subroutine oil_tracer_end

!> \namespace oil_tracer
!!
!!  By Alistair Adcroft and Robert Hallberg, 2010                                           *
!!
!!    In the midst of the Deepwater Horizon oil spill, it became evident that
!!  models were needed to predict the long-term fate of dissolved oil in the
!!  open ocean.  This tracer packages mimics the transport, dilution and decay
!!  of dissolved oil plumes in the ocean.
!!
!!    This tracer package was central to the simulations used by Adcroft et al.,
!!  GRL 2010, to prove that the Deepwater Horizon spill was an important regional
!!  event, with implications for dissolved oxygen levels in the Gulf of Mexico,
!!  but not one that would directly impact the East Coast of the U.S.

end module oil_tracer