6. Host Side Coding

This chapter describes the connection of a host model with the pool of CCPP Physics schemes through the CCPP Framework.

6.1. Variable Requirements on the Host Model Side

All variables required to communicate between the host model and the physics, as well as to communicate between physics schemes, need to be allocated by the host model. An exception is variables errflg, errmsg, loop_cnt, loop_max, blk_no, and thrd_no, which are allocated by the CCPP Framework, as explained in Section 6.4.1. See Section 2.3 for information about the variables required for the current pool of CCPP physics.

At present, only two types of variable definitions are supported by the CCPP Framework:

  • Standard Fortran variables (character, integer, logical, real) defined in a module or in the main program. For character variables, a fixed length is required. All others can have a kind attribute of a kind type defined by the host model.

  • Derived data types (DDTs) defined in a module or the main program. While the use of DDTs as arguments to physics schemes in general is discouraged (see Section 2.4), it is perfectly acceptable for the host model to define the variables requested by physics schemes as components of DDTs and pass these components to CCPP by using the correct local_name (e.g., myddt%thecomponentIwant; see Section 6.2.)

6.2. Metadata for Variables in the Host Model

To establish the link between host model variables and physics scheme variables, the host model must provide metadata information similar to those presented in Section 2.2. The host model can have multiple metadata files (.meta), each with the required [ccpp-table-properties] section and the related [ccpp-arg-table] sections. The host model Fortran files contain three-line snippets to indicate the location for insertion of the metadata information contained in the corresponding section in the .meta file.

!!> \section arg_table_example_vardefs
!! \htmlinclude example_vardefs.html
!!

For each variable required by the pool of CCPP Physics schemes, one and only one entry must exist on the host model side. The connection between a variable in the host model and in the physics scheme is made through its standard_name.

The following requirements must be met when defining metadata for variables in the host model (see also Listing 6.1 and Listing 6.2 for examples of host model metadata).

  • The standard_name must match that of the target variable in the physics scheme.

  • The type, kind, shape and size of the variable (as defined in the host model Fortran code) must match that of the target variable.

  • The attributes units, rank, type and kind in the host model metadata must match those in the physics scheme metadata.

  • The attribute active is used to allocate variables under certain conditions. It must be written as a Fortran expression that equates to .true. or .false., using the CCPP standard names of variables. active attributes for all variables are .true. by default. See Section 6.2.2 for details.

  • The intent attribute is not a valid attribute for host model metadata and will be ignored, if present.

  • The local_name of the variable must be set to the name the host model cap uses to refer to the variable.

  • The metadata section that exposes a DDT to the CCPP (as opposed to the section that describes the components of a DDT) must be in the same module where the memory for the DDT is allocated. If the DDT is a module variable, then it must be exposed via the module’s metadata section, which must have the same name as the module.

  • Metadata sections describing module variables must be placed inside the module.

  • Metadata sections describing components of DDTs must be placed immediately before the type definition and have the same name as the DDT.

    module example_vardefs

      implicit none

!!> \section arg_table_example_vardefs
!! \htmlinclude example_vardefs.html
!!

      integer, parameter           :: r15 = selected_real_kind(15)
      integer                      :: ex_int
      real(kind=8), dimension(:,:) :: ex_real1
      character(len=64)            :: errmsg
      logical                      :: errflg

!!> \section arg_table_example_ddt
!! \htmlinclude example_ddt.html
!!

      type ex_ddt
        logical              :: l
        real, dimension(:,:) :: r
      end type ex_ddt

      type(ex_ddt) :: ext

    end module example_vardefs

Listing 6.1: Example host model file with reference to metadata. In this example, both the definition and the declaration (memory allocation) of a DDT ext (of type ex_ddt ) are in the same module.

########################################################################
[ccpp-table-properties]
  name = arg_table_example_vardefs
  type = module

[ccpp-arg-table]
  name = arg_table_example_vardefs
  type = module
[ex_int]
  standard_name = example_int
  long_name = ex. int
  units = none
  dimensions = ()
  type = integer
[ex_real]
  standard_name = example_real
  long_name = ex. real
  units = m
  dimensions = (horizontal_loop_extent,vertical_layer_dimension)
  type = real
  kind = kind=8
[ex_ddt]
  standard_name = example_ddt
  long_name = ex. ddt
  units = DDT
  dimensions = ()
  type = ex_ddt
[ext]
  standard_name = example_ddt_instance
  long_name = ex. ddt inst
  units = DDT
  dimensions = ()
  type = ex_ddt
[errmsg]
  standard_name = ccpp_error_message
  long_name = error message for error handling in CCPP
  units = none
  dimensions = ()
  type = character
  kind = len=64
[errflg]
  standard_name = ccpp_error_code
  long_name = error code for error handling in CCPP
  units = 1
  dimensions = ()
  type = integer

########################################################################
[ccpp-table-properties]
  name = arg_table_example_ddt
  type = ddt

[ccpp-arg-table]
  name = arg_table_example_ddt
  type = ddt
[ext%1]
  standard_name = example_flag
  long_name = ex. flag
  units = flag
  dimensions =
  type = logical
[ext%r]
  standard_name = example_real3
  long_name = ex. real
  units = kg
  dimensions = (horizontal_loop_extent,vertical_layer_dimension)
  type = real
  kind = r15
[ext%r(;,1)]
  standard_name = example_slice
  long_name = ex. slice
  units = kg
  dimensions = (horizontal_loop_extent,vertical_layer_dimension)
  type = real
  kind = r15
[nwfa2d]
  standard_name = tendency_of_water_friendly_aerosols_at_surface
  long_name = instantaneous water-friendly sfc aerosol source
  units = kg-1 s-1
  dimensions = (horizontal_loop_extent)
  type = real
  kind = kind_phys
  active = (flag_for_microphysics_scheme == flag_for_thompson_microphysics_scheme .and. flag_for_aerosol_physics)
[qgrs(:,:,index_for_water_friendly_aerosols)]
  standard_name = water_friendly_aerosol_number_concentration
  long_name = number concentration of water-friendly aerosols
  units = kg-1
  dimensions = (horizontal_loop_extent,vertical_layer_dimension)
  active = (index_for_water_friendly_aerosols > 0)
  type = real
  kind = kind_phys

Listing 6.2: Example host model metadata file ( .meta ).

6.2.1. horizontal_dimension vs. horizontal_loop_extent

Please refer to section Section 2.2.3 for a description of the differences between horizontal_dimension and horizontal_loop_extent. The host model must define both variables to represent the horizontal dimensions in use by the physics in the metadata.

For the examples in listing Listing 6.2, the host model stores all horizontal grid columns of each variable in one contiguous block, and the variables horizontal_dimension and horizontal_loop_extent are identical. Alternatively, a host model could store (non-contiguous) blocks of data in an array of DDTs with a length of the total number of blocks, as shown in listing Listing 6.3. Figure 3.1 depicts the differences in variable allocation for these two cases.

########################################################################
[ccpp-table-properties]
  name = arg_table_example_vardefs
  type = module

[ccpp-arg-table]
  name = arg_table_example_vardefs
  type = module
...
[ex_ddt]
  standard_name = example_ddt
  long_name = ex. ddt
  units = DDT
  dimensions = ()
  type = ex_ddt
[ext(ccpp_block_number)]
  standard_name = example_ddt_instance
  long_name = ex. ddt inst
  units = DDT
  dimensions = ()
  type = ex_ddt
[ext]
  standard_name = example_ddt_instance_all_blocks
  long_name = ex. ddt inst
  units = DDT
  dimensions = (ccpp_block_count)
  type = ex_ddt
...

########################################################################
[ccpp-table-properties]
  name = arg_table_example_ddt
  type = ddt

[ccpp-arg-table]
  name = arg_table_example_ddt
  type = ddt
[ext%1]
  standard_name = example_flag
  long_name = ex. flag
  units = flag
  dimensions =
  type = logical
[ext%r]
  standard_name = example_real3
  long_name = ex. real
  units = kg
  dimensions = (horizontal_loop_extent,vertical_layer_dimension)
  type = real
  kind = r15
...

Listing 6.3: Example host model metadata file ( .meta ) for a host model using blocked data structures.

_images/ccpp_blocked_data.png

Fig. 6.1 This figure depicts the difference between non-blocked (contiguous) and blocked data structures.

When blocked data structures are used by the host model, horizontal_loop_extent corresponds to the block size, and the sum of all block sizes equals horizontal_dimension. In either case, the correct horizontal dimension for host model variables is horizontal_loop_extent. In the time integration (run) phase, the physics are called for one block at a time (although possibly in parallel using OpenMP threading). In all other phases, the CCPP Framework automatically combines the discontiguous blocked data into contiguous arrays before calling into a physics scheme, as shown in Listing 6.4.

allocate(bar_local(1:ncolumns))
ib = 1
do nb=1,nblocks
  bar_local(ib:ib+blocksize(nb)-1) = foo(nb)%bar
  ib = ib+blocksize(nb)
end do

call myscheme_init(bar=bar_local)

ib = 1
do nb=1,nblocks
  foo(nb)%bar = bar_local(ib:ib+blocksize(nb)-1)
  ib = ib+blocksize(nb)
end do
deallocate(bar_local)

Listing 6.4: Automatic combination of blocked data structures in the auto-generated caps

6.2.2. Active Attribute

The CCPP must be able to detect when arrays need to be allocated, and when certain tracers must be present in order to perform operations or tests in the auto-generated caps (e.g. unit conversions, blocked data structure copies, etc.). This is accomplished with the attribute active in the metadata for the host model variables (e.g., GFS_typedefs.meta for the UFS Atmosphere or the SCM).

Several arrays in the host model (e.g., GFS_typedefs.F90 in the UFS Atmosphere or the SCM) are allocated based on certain conditions, for example:

!--- needed for Thompson's aerosol option
if(Model%imp_physics == Model%imp_physics_thompson .and. Model%ltaerosol) then
  allocate (Coupling%nwfa2d (IM))
  allocate (Coupling%nifa2d (IM))
  Coupling%nwfa2d   = clear_val
  Coupling%nifa2d   = clear_val
endif

Other examples are the elements in the tracer array, where their presence depends on the corresponding index being larger than zero. For example:

integer              :: ntwa            !< tracer index for water friendly aerosol
...
Model%ntwa             = get_tracer_index(Model%tracer_names, 'liq_aero', ...)
...
if (Model%ntwa>0) then
  ! do something with qgrs(:,:,Model%ntwa)
end if

The active attribute is a conditional statement that, if true, will allow the corresponding variable to be allocated. It must be written as a Fortran expression that equates to .true. or .false., using the CCPP standard names of variables. Active attributes for all variables are .true. by default.

If a developer adds a new variable that is only allocated under certain conditions, or changes the conditions under which an existing variable is allocated, a corresponding change must be made in the metadata for the host model variables (GFS_typedefs.meta for the UFS Atmosphere or the SCM). See variables nwfa2d and qgrs in Listing 6.2 for an example.

6.3. CCPP Variables in the SCM and UFS Atmosphere Host Models

While the use of standard Fortran variables is preferred, in the current implementation of the CCPP in the UFS Atmosphere and in the SCM almost all data is contained in DDTs for organizational purposes. In the case of the SCM, DDTs are defined in gmtb_scm_type_defs.f90 and GFS_typedefs.F90, and in the case of the UFS Atmosphere, they are defined in both GFS_typedefs.F90 and CCPP_typedefs.F90. The current implementation of the CCPP in both host models uses the following set of DDTs:

  • GFS_init_type variables to allow proper initialization of GFS physics

  • GFS_statein_type prognostic state data provided by dycore to physics

  • GFS_stateout_type prognostic state after physical parameterizations

  • GFS_sfcprop_type surface properties read in and/or updated by climatology, obs, physics

  • GFS_coupling_type fields from/to coupling with other components, e.g., land/ice/ocean

  • GFS_control_type control parameters input from a namelist and/or derived from others

  • GFS_grid_type grid data needed for interpolations and length-scale calculations

  • GFS_tbd_type data not yet assigned to a defined container

  • GFS_cldprop_type cloud properties and tendencies needed by radiation from physics

  • GFS_radtend_type radiation tendencies needed by physics

  • GFS_diag_type fields targeted for diagnostic output to disk

  • GFS_interstitial_type fields used to communicate variables among schemes in the slow physics group required to replace interstitial code that resided in GFS_{physics, radiation}_driver.F90 in IPD

  • GFS_data_type combined type of all of the above except GFS_control_type and GFS_interstitial_type

  • CCPP_interstitial_type fields used to communicate variables among schemes in the fast physics group

The DDT descriptions provide an idea of what physics variables go into which data type. GFS_diag_type can contain variables that accumulate over a certain amount of time and are then zeroed out. Variables that require persistence from one timestep to another should not be included in the GFS_diag_type nor the GFS_interstitial_type DDTs. Similarly, variables that need to be shared between groups cannot be included in the GFS_interstitial_type DDT. Although this memory management is somewhat arbitrary, new variables provided by the host model or derived in an interstitial scheme should be put in a DDT with other similar variables.

Each DDT contains a create method that allocates the data defined using the metadata. For example, the GFS_stateout_type contains:

type GFS_stateout_type

   !-- Out (physics only)
   real (kind=kind_phys), pointer :: gu0 (:,:)   => null()  !< updated zonal wind
   real (kind=kind_phys), pointer :: gv0 (:,:)   => null()  !< updated meridional wind
   real (kind=kind_phys), pointer :: gt0 (:,:)   => null()  !< updated temperature
   real (kind=kind_phys), pointer :: gq0 (:,:,:) => null()  !< updated tracers

   contains
     procedure :: create  => stateout_create  !<   allocate array data
 end type GFS_stateout_type

In this example, gu0, gv0, gt0, and gq0 are defined in the host-side metadata section, and when the subroutine stateout_create is called, these arrays are allocated and initialized to zero. With the CCPP, it is possible to not only refer to components of DDTs, but also to slices of arrays with provided metadata as long as these are contiguous in memory. An example of an array slice from the GFS_stateout_type looks like:

########################################################################
[ccpp-table-properties]
   name = GFS_stateout_type
   type = ddt
   dependencies =

 [ccpp-arg-table]
   name = GFS_stateout_type
   type = ddt
 [gq0(:,:,index_for_snow_water)]
   standard_name = snow_water_mixing_ratio_updated_by_physics
   long_name = moist (dry+vapor, no condensates) mixing ratio of snow water updated by physics
   units = kg kg-1
   dimensions = (horizontal_loop_extent,vertical_layer_dimension)
   type = real
   kind = kind_phys

Array slices can be used by physics schemes that only require certain values from an array.

6.4. CCPP API

The CCPP Application Programming Interface (API) is comprised of a set of clearly defined methods used to communicate variables between the host model and the physics and to run the physics. The API is automatically generated by the CCPP prebuild script (see Chapter 8) and contains the subroutines ccpp_physics_init, ccpp_physics_timestep_init, ccpp_physics_run, ccpp_physics_timestep_finalize, and ccpp_physics_finalize (described below).

6.4.1. Data Structure to Transfer Variables between Dynamics and Physics

The cdata structure is used for holding six variables that must always be available to the physics schemes. These variables are listed in a metadata table in ccpp-framework/src/ccpp_types.meta (Listing 6.5).

  • Error code for handling in CCPP (errmsg).

  • Error message associated with the error code (errflg).

  • Loop counter for subcycling loops (loop_cnt).

  • Loop extent for subcycling loops (loop_max).

  • Number of block for explicit data blocking in CCPP (blk_no).

  • Number of thread for threading in CCPP (thrd_no).

[ccpp-table-properties]
  name = ccpp_types
  type = module
  dependencies =

[ccpp-arg-table]
  name = ccpp_types
  type = module
[ccpp_t]
  standard_name = ccpp_t
  long_name = definition of type ccpp_t
  units = DDT
  dimensions = ()
  type = ccpp_t

########################################################################
[ccpp-table-properties]
  name = ccpp_t
  type = ddt
  dependencies =

[ccpp-arg-table]
  name = ccpp_t
  type = ddt
[errflg]
  standard_name = ccpp_error_code
  long_name = error code for error handling in CCPP
  units = 1
  dimensions = ()
  type = integer
[errmsg]
  standard_name = ccpp_error_message
  long_name = error message for error handling in CCPP
  units = none
  dimensions = ()
  type = character
  kind = len=512
[loop_cnt]
  standard_name = ccpp_loop_counter
  long_name = loop counter for subcycling loops in CCPP
  units = index
  dimensions = ()
  type = integer
[loop_max]
  standard_name = ccpp_loop_extent
  long_name = loop extent for subcycling loops in CCPP
  units = count
  dimensions = ()
  type = integer
[blk_no]
  standard_name = ccpp_block_number
  long_name = number of block for explicit data blocking in CCPP
  units = index
  dimensions = ()
  type = integer
[thrd_no]
  standard_name = ccpp_thread_number
  long_name = number of thread for threading in CCPP
  units = index
  dimensions = ()
  type = integer

Listing 6.5: Mandatory variables provided by the CCPP Framework from ccpp-framework/src/ccpp_types.meta . These variables must not be defined by the host model.

Two of the variables are mandatory and must be passed to every physics scheme: errmsg and errflg. The variables loop_cnt, loop_max, blk_no, and thrd_no can be passed to the schemes if required, but are not mandatory. They are, however, required for the auto-generated caps to pass the correct data to the physics and to realize the subcycling of schemes. The cdata structure is only used to hold these six variables, since the host model variables are directly passed to the physics without the need for an intermediate data structure.

Note that cdata is not restricted to being a scalar but can be a multidimensional array, depending on the needs of the host model. For example, a model that uses a one-dimensional array of blocks for better cache-reuse and OpenMP threading to process these blocks in parallel may require cdata to be a two-dimensional array of size “number of blocks” x “number of OpenMP threads”.

6.4.2. Initializing and Finalizing the CCPP

At the beginning of each run, the cdata structure needs to be set up. Similarly, at the end of each run, it needs to be terminated. This is done with subroutines ccpp_init and ccpp_finalize. These subroutines should not be confused with ccpp_physics_init and ccpp_physics_finalize, which were described in Chapter 5.

Note that optional arguments are denoted with square brackets.

6.4.2.1. Suite Initialization

The suite initialization step consists of allocating (if required) and initializing the cdata structure(s), it does not call the CCPP Physics or any auto-generated code. The simplest example is a suite initialization step that consists of initializing a scalar cdata instance with cdata%blk_no = 1 and cdata%thrd_no = 1.

A more complicated example is when multiple cdata structures are in use, namely one for the the CCPP phases that require access to all data of an MPI task (a scalar that is initialized in the same way as above), and one for the run phase, where chunks of blocked data are processed in parallel by multiple OpenMP threads, as shown in Listing Listing 6.6.

...

type(ccpp_t),                              target :: cdata_domain
type(ccpp_t), dimension(:,:), allocatable, target :: cdata_block

! ccpp_suite is set during the namelist read by the host model
character(len=256) :: ccpp_suite
integer            :: nthreads

...

! Get and set number of OpenMP threads (module
! variable) that are available to run physics
nthreads = omp_get_max_threads()

! For physics running over the entire domain,
! block and thread number are not used
cdata_domain%blk_no  = 1
cdata_domain%thrd_no = 1

! Allocate cdata structure for blocks and threads
allocate(cdata_block(1:nblks,1:nthreads))

! Assign the correct block and thread numbers
do nt=1,nthreads
  do nb=1,nblks
    cdata_block(nb,nt)%blk_no = nb
    cdata_block(nb,nt)%thrd_no = nt
  end do
end do

Listing 6.6: A morre complex suite initialization step that consists of allocating and initializing multiple ``cdata`` structures.

Depending on the implementation of CCPP in the host model, the suite name for the suite to be executed must be set in this step as well (omitted in Listing Listing 6.6).

6.4.2.2. Suite Finalization

The suite finalization consists of deallocating any cdata structures, if applicable, and optionally resetting scalar cdata instances as in the following example for the UFS:

deallocate(cdata_block)
! Optional
cdata_domain%blk_no = -999
cdata_domain%thrd_no = -999
...

6.4.3. Running the Physics

The physics is invoked by calling subroutine ccpp_physics_run. This subroutine is part of the CCPP API and is auto-generated. This subroutine is capable of executing the physics with varying granularity, that is, a single group, or an entire suite can be run with a single subroutine call. Typical calls to ccpp_physics_run are below,where suite_name is mandatory and group_name is optional:

call ccpp_physics_run(cdata, suite_name, [group_name], ierr=ierr)

6.4.4. Initializing and Finalizing the Physics

Many (but not all) physical parameterizations need to be initialized, which includes functions such as reading lookup tables, reading input datasets, computing derived quantities, broadcasting information to all MPI ranks, etc. Initialization procedures are done for the entire domain, that is, they are not subdivided by blocks and need access to all data that an MPI task owns. Similarly, many (but not all) parameterizations need to be finalized, which includes functions such as deallocating variables, resetting flags from initialized to non-initialized, etc. Initialization and finalization functions are each performed once per run, before the first call to the physics and after the last call to the physics, respectively. They may not contain thread-dependent or block-dependent information.

The initialization and finalization can be invoked for a single group, or for the entire suite. In both cases, subroutines ccpp_physics_init and ccpp_physics_finalize are used and the arguments passed to those subroutines determine the type of initialization.

6.4.4.1. Subroutine ccpp_physics_init

This subroutine is part of the CCPP API and is auto-generated. A typical call to ccpp_physics_init is:

call ccpp_physics_init(cdata, suite_name, [group_name], ierr=ierr)

6.4.4.2. Subroutine ccpp_physics_finalize

This subroutine is part of the CCPP API and is auto-generated. A typical call to ccpp_physics_finalize is:

call ccpp_physics_finalize(cdata, suite_name, [group_name], ierr=ierr)

6.4.5. Initializing and Finalizing the time step

The time step initialization typically consists of updating quantities that depend on the valid time, for example solar insulation angle, aerosol emission rates and other values obtained from climatologies. Like the physics initialization and finalization steps, the time step intialization and finalization steps need access to the entire data of an MPI task and may not contain thread-dependent or block-dependent information.

6.4.5.1. Subroutine ccpp_physics_timestep_init

This subroutine is part of the CCPP API and is auto-generated.A typical call to ccpp_physics_timestep_init is:

call ccpp_physics_timestep_init(cdata, suite_name, [group_name], ierr=ierr)

6.4.5.2. Subroutine ccpp_physics_timestep_finalize

This subroutine is part of the CCPP API and is auto-generated. A typical call to ccpp_physics_timestep_finalize is:

call ccpp_physics_timestep_finalize(cdata, suite_name, [group_name], ierr=ierr)

6.5. Host Caps

The purpose of the host model cap is to abstract away the communication between the host model and the CCPP Physics schemes. While CCPP calls can be placed directly inside the host model code (as is done for the relatively simple SCM), it is recommended to separate the cap in its own module for clarity and simplicity (as is done for the UFS Atmosphere). While the details of implementation will be specific to each host model, the host model cap is responsible for the following general functions:

  • Allocating memory for variables needed by physics

    • All variables needed to communicate between the host model and the physics, and all variables needed to communicate among physics schemes, need to be allocated by the host model. The latter, for example for interstitial variables used exclusively for communication between the physics schemes, are typically allocated in the cap.

  • Allocating and initializing the cdata structure(s) and setting the suite name (suite initialization)

  • Providing interfaces to call the CCPP

    • The cap must provide functions or subroutines that can be called at the appropriate places in the host model time integration loop and that internally call ccpp_physics_init, ccpp_physics_timestep_init, ccpp_physics_run, ccpp_physics_timestep_finalize and ccpp_physics_finalize, and handle any errors returned. Listing 6.7 provides an example where the host cap consists of three subroutines physics_init (which consists of the suite initialization and CCPP physics init phase), physics_run (which internally performs the CCPP time step init, run, and time step finalize phases), and physics_finalize (which consists of the suite finalization and CCPP physics finalize phase).

module example_ccpp_host_cap

 use ccpp_types,         only: ccpp_t
 use ccpp_static_api,    only: ccpp_physics_init,              &
                               ccpp_physics_timestep_init,     &
                               ccpp_physics_run,               &
                               ccpp_physics_timestep_finalize, &
                               ccpp_physics_finalize

  implicit none
  ! CCPP data structure
  type(ccpp_t), save, target :: cdata
  public :: physics_init, physics_run, physics_finalize
contains

 subroutine physics_init(ccpp_suite_name)
   character(len=*), intent(in) :: ccpp_suite_name
   integer :: ierr
   ierr = 0

   ! Initialize cdata
   cdata%blk_no = 1
   cdata%thrd_no = 1

   ! Initialize CCPP physics (run all _init routines)
   call ccpp_physics_init(cdata, suite_name=trim(ccpp_suite_name),      &
                          ierr=ierr)

 end subroutine physics_init

 subroutine physics_run(ccpp_suite_name, group)
   ! Optional argument group can be used to run a group of schemes      &
   ! defined in the SDF. Otherwise, run entire suite.
   character(len=*),           intent(in) :: ccpp_suite_name
   character(len=*), optional, intent(in) :: group

   integer :: ierr
   ierr = 0

   if (present(group)) then
      call ccpp_physics_timestep_init(cdata,                            &
                            suite_name=trim(ccpp_suite_name),           &
                            group_name=group, ierr=ierr)
      call ccpp_physics_run(cdata, suite_name=trim(ccpp_suite_name),    &
                            group_name=group, ierr=ierr)
      call ccpp_physics_timestep_finalize(cdata,                        &
                            suite_name=trim(ccpp_suite_name),           &
                            group_name=group, ierr=ierr)
   else
      call ccpp_physics_timestep_init(cdata,                            &
                            suite_name=trim(ccpp_suite_name), ierr=ierr)
      call ccpp_physics_run(cdata, suite_name=trim(ccpp_suite_name),    &
                            ierr=ierr)
      call ccpp_physics_timestep_finalize(cdata,                        &
                            suite_name=trim(ccpp_suite_name), ierr=ierr)
   end if

 end subroutine physics_run

 subroutine physics_finalize(ccpp_suite_name)
   character(len=*), intent(in) :: ccpp_suite_name
   integer :: ierr
   ierr = 0

   ! Finalize CCPP physics (run all _finalize routines)
   call ccpp_physics_finalize(cdata, suite_name=trim(ccpp_suite_name),  &
                              ierr=ierr)

   ! Reset cdata
   cdata%blk_no = -999
   cdata%thrd_no = -999

 end subroutine physics_finalize

end module example_ccpp_host_cap

Listing 6.7: Fortran template for a CCPP host model cap. After each call to ``ccpp_physics_*``, the host model should check the return code ``ierr`` and handle any errors (omitted for readability).

Readers are referred to the actual implementations of the cap functions in the CCPP-SCM and the UFS for further information. For the SCM, the cap functions are implemented in:

  • ccpp-scm/scm/src/scm.F90

  • ccpp-scm/scm/src/scm_type_defs.F90

  • ccpp-scm/scm/src/scm_setup.F90

  • ccpp-scm/scm/src/scm_time_integration.F90

For the UFS, the cap functions can be found in ufs-weather-model/FV3/ccpp/driver/CCPP_driver.F90.