Obc setup plus segment update period (#198)

* Setup OBC segments for COBALT/OBGC tracers

    - These are updates required to setup OBC segments for OBGC tracers.
    - Since COBALT package has more than 50 tracers using the MOM6 table
      mechanism for setting up OBC segments is not feasible. Rather, this
      update delegates such setup to mechanims used in ocean_BGS tracers
      leaving MOM6 mechanism for native tracers intact.
    - Fixed issues caught by MOM6 githubCI

* Add capability to change obc segment update period

- COBALT tracers do not need as frequent segment bc updates and can
  use a larger update period to speed up the model.
  This commit introduces a new parameter DT_OBC_SEG_UPDATE_OBGC
  that can be adjusted for obc segment update period.
- This commit applies the change only to BGC tracers but can easily
  be changed to apply for all.

* Insert missing US%T_to_sec

- The unit conversion factor was missing causing a crash in a newer test.

* Updates from Andrew Ross

- Avoid low initial values in the tracer reservoirs

* Per Andrew Ross review

* corrected indentation per review

* Avoid using module vars per review request

- Reviewer asked to avoid using module variables with "save" attributes.
- This commit hides the module variables inside the existing OBC type.

* Coding style corrections per review

* Modification per review: do_not_log if .not.associated(CS%OBC)

Co-authored-by: Robert Hallberg <[email protected]>

config_src/external/GFDL_ocean_BGC/generic_tracer_utils.F90

@@ -25,6 +25,8 @@ module g_tracer_utils
     character(len=fm_string_len) :: src_var_name !< Tracer source variable name
     character(len=fm_string_len) :: src_var_unit !< Tracer source variable units
     character(len=fm_string_len) :: src_var_gridspec !< Tracer source grid file name
+    character(len=fm_string_len) :: obc_src_file_name !< Boundary condition tracer source filename
+    character(len=fm_string_len) :: obc_src_field_name !< Boundary condition tracer source fieldname
     integer :: src_var_record !< Unknown
     logical :: requires_src_info = .false. !< Unknown
     real    :: src_var_unit_conversion = 1.0 !< This factor depends on the tracer. Ask Jasmin
@@ -61,6 +63,7 @@ module g_tracer_utils
   public :: g_tracer_get_next
   public :: g_tracer_is_prog
   public :: g_diag_type
+  public :: g_tracer_get_obc_segment_props
 
   !> Set the values of various (array) members of the tracer node g_tracer_type
   !!
@@ -284,6 +287,17 @@ subroutine g_tracer_get_next(g_tracer,g_tracer_next)
     type(g_tracer_type), pointer :: g_tracer_next !< Pointer to the next tracer node in the list
   end subroutine g_tracer_get_next
 
+  !> get obc segment properties for each tracer
+  subroutine g_tracer_get_obc_segment_props(g_tracer_list, name, obc_has, src_file, src_var_name,lfac_in,lfac_out)
+    type(g_tracer_type), pointer         :: g_tracer_list !< pointer to the head of the generic tracer list
+    character(len=*),         intent(in) :: name          !< tracer name
+    logical,                  intent(out):: obc_has       !< .true. if This tracer has OBC
+    real,            optional,intent(out):: lfac_in       !< OBC reservoir inverse lengthscale factor
+    real,            optional,intent(out):: lfac_out      !< OBC reservoir inverse lengthscale factor
+    character(len=*),optional,intent(out):: src_file      !< OBC source file
+    character(len=*),optional,intent(out):: src_var_name  !< OBC source variable in file
+  end subroutine g_tracer_get_obc_segment_props
+
   !>Vertical Diffusion of a tracer node
   !!
   !! This subroutine solves a tridiagonal equation to find and set values of vertically diffused field

src/core/MOM.F90

@@ -133,7 +133,7 @@ module MOM
 use MOM_tracer_registry,       only : lock_tracer_registry, tracer_registry_end
 use MOM_tracer_flow_control,   only : call_tracer_register, tracer_flow_control_CS
 use MOM_tracer_flow_control,   only : tracer_flow_control_init, call_tracer_surface_state
-use MOM_tracer_flow_control,   only : tracer_flow_control_end
+use MOM_tracer_flow_control,   only : tracer_flow_control_end, call_tracer_register_obc_segments
 use MOM_transcribe_grid,       only : copy_dyngrid_to_MOM_grid, copy_MOM_grid_to_dyngrid
 use MOM_unit_scaling,          only : unit_scale_type, unit_scaling_init
 use MOM_unit_scaling,          only : unit_scaling_end, fix_restart_unit_scaling
@@ -294,7 +294,11 @@ module MOM
                                      !! barotropic time step [s]. If this is negative dtbt is never
                                      !! calculated, and if it is 0, dtbt is calculated every step.
   type(time_type) :: dtbt_reset_interval !< A time_time representation of dtbt_reset_period.
-  type(time_type) :: dtbt_reset_time !< The next time DTBT should be calculated.
+  type(time_type) :: dtbt_reset_time     !< The next time DTBT should be calculated.
+  real            :: dt_obc_seg_period   !< The time interval between OBC segment updates for OBGC tracers
+  type(time_type) :: dt_obc_seg_interval !< A time_time representation of dt_obc_seg_period.
+  type(time_type) :: dt_obc_seg_time     !< The next time OBC segment update is applied to OBGC tracers.
+
   real, dimension(:,:), pointer :: frac_shelf_h => NULL() !< fraction of total area occupied
   !! by ice shelf [nondim]
   real, dimension(:,:), pointer :: mass_shelf => NULL() !< Mass of ice shelf [R Z ~> kg m-2]
@@ -1132,6 +1136,17 @@ subroutine step_MOM_dynamics(forces, p_surf_begin, p_surf_end, dt, dt_thermo, &
     call disable_averaging(CS%diag)
   endif
 
+  !OBC segment data update for some fields can be less frequent than others
+  if(associated(CS%OBC)) then
+    CS%OBC%update_OBC_seg_data = .false.
+    if (CS%dt_obc_seg_period == 0.0) CS%OBC%update_OBC_seg_data = .true.
+    if (CS%dt_obc_seg_period > 0.0) then
+      if (Time_local >= CS%dt_obc_seg_time) then
+        CS%OBC%update_OBC_seg_data = .true.
+        CS%dt_obc_seg_time = CS%dt_obc_seg_time + CS%dt_obc_seg_interval
+      endif
+    endif
+  endif
 
   if (CS%do_dynamics .and. CS%split) then !--------------------------- start SPLIT
     ! This section uses a split time stepping scheme for the dynamic equations,
@@ -2152,6 +2167,13 @@ subroutine initialize_MOM(Time, Time_init, param_file, dirs, CS, restart_CSp, &
                  units="s", default=default_val, do_not_read=(dtbt > 0.0))
   endif
 
+  CS%dt_obc_seg_period = -1.0
+  call get_param(param_file, "MOM", "DT_OBC_SEG_UPDATE_OBGC", CS%dt_obc_seg_period, &
+               "The time between OBC segment data updates for OBGC tracers. "//&
+               "This must be an integer multiple of DT and DT_THERM. "//&
+               "The default is set to DT.", &
+               units="s", default=US%T_to_s*CS%dt, do_not_log=.not.associated(CS%OBC))
+
   ! This is here in case these values are used inappropriately.
   use_frazil = .false. ; bound_salinity = .false.
   CS%tv%P_Ref = 2.0e7*US%kg_m3_to_R*US%m_s_to_L_T**2
@@ -2627,6 +2649,8 @@ subroutine initialize_MOM(Time, Time_init, param_file, dirs, CS, restart_CSp, &
     ! could occur with the call to update_OBC_data or after the main initialization.
     if (use_temperature) &
       call register_temp_salt_segments(GV, US, CS%OBC, CS%tracer_Reg, param_file)
+    !This is the equivalent call to register_temp_salt_segments for external tracers with OBC
+    call call_tracer_register_obc_segments(GV, param_file, CS%tracer_flow_CSp, CS%tracer_Reg, CS%OBC)
 
     ! This needs the number of tracers and to have called any code that sets whether
     ! reservoirs are used.
@@ -2962,6 +2986,12 @@ subroutine initialize_MOM(Time, Time_init, param_file, dirs, CS, restart_CSp, &
             CS%ntrunc, cont_stencil=CS%cont_stencil)
   endif
 
+  !Set OBC segment data update period
+  if (associated(CS%OBC) .and. CS%dt_obc_seg_period > 0.0) then
+    CS%dt_obc_seg_interval = real_to_time(US%T_to_s*CS%dt_obc_seg_period)
+    CS%dt_obc_seg_time = Time + CS%dt_obc_seg_interval
+  endif
+
   call callTree_waypoint("dynamics initialized (initialize_MOM)")
 
   CS%mixedlayer_restrat = mixedlayer_restrat_init(Time, G, GV, US, param_file, diag, &