MODULE dart_pop_mod (POP)¶

Overview¶

dart_pop_mod provides a consistent collection of routines that are useful for multiple programs e.g. dart_to_pop, pop_to_dart, etc.

Namelist¶

There are no namelists unique to this module. It is necessary for this module to read some of the POP namelists, and so they are declared in this module. In one instance, DART will read the time_manager_nml namelist and write an updated version to control the length of the integration of POP. All other information is simply read from the namelists and is used in the same context as POP itself. The POP documentation should be consulted. Only the variables of interest to DART are described in this document.

All namelists are read from a file named pop_in.

namelist /time_manager_nml/  allow_leapyear, stop_count, stop_option

dart_to_pop controls the model advance of LANL/POP by creating a &time_manager_nml in pop_in.DART IFF the DART state being converted has the ‘advance_to_time’ record. The pop_in.DART must be concatenated with the other namelists needed by POP into a file called pop_in . We have chosen to store the other namelists (which contain static information) in a file called pop_in.part2. Initially, the time_manager_nml is stored in a companion file called pop_in.part1 and the two files are concatenated into the expected pop_in - then, during the course of an assimilation experiment, DART keeps writing out a new time_manager_nml with new integration information - which gets appended with the static information in pop_in.part2

Contents	Type	Description
allow_leapyear	logical	DART ignores the setting of this parameter. All observations must use a Gregorian calendar. There are pathological cases, but if you are doing data assimilation, just use the Gregorian calendar. [default: .true.]
stop_count	integer	the number of model advance steps to take. [default: 1]
stop_option	character(len=64)	The units for the number of model advance steps (`stop_count`) to take. [default: ‘ndays’]

namelist /io_nml/  luse_pointer_files, pointer_filename

Contents	Type	Description
luse_pointer_files	logical	switch to indicate the use of pointer files or not. If `.true.`, a pointer file is used to contain the name of the restart file to be used. DART requires this to be `.true`. [default: .true.]
pointer_filename	character(len=100)	The name of the pointer file. All of the DART scripts presume and require the use of the default. Each ensmeble member gets its own pointer file. [default: rpointer.ocn.[1-N].restart]

namelist /restart_nml/  restart_freq_opt, restart_freq

Contents	Type	Description
luse_pointer_files	logical	switch to indicate the use of pointer files or not. If `.true.`, a pointer file is used to contain the name of the restart file to be used. DART requires this to be `.true`. [default: .true.]
pointer_filename	character(len=100)	The name of the pointer file. All of the DART scripts presume and require the use of the default. Each ensmeble member gets its own pointer file. [default: rpointer.ocn.[1-N].restart]

namelist /init_ts_nml/  init_ts_option, init_ts_file, init_ts_file_fmt

The dart_pop_mod:initialize_module() routine reads pop_in . There are several code stubs for future use that may allow for a more fully-supported POP namelist implementation. This namelist is one of them. Until further notice, the init_ts_nml is completely ignored by DART.

Contents	Type	Description
init_ts_option	character(len=64)	NOT USED by DART. All T,S information comes from a netCDF restart file named `pop.r.nc` [default: ‘restart’]
init_ts_file	character(len=100)	NOT USED by DART. All T,S information comes from `pop.r.nc` [default: ‘pop.r’]
init_ts_file_fmt	character(len=64)	NOT USED by DART. The file format is `'nc'` [default: ‘nc’]

namelist /domain_nml/  ew_boundary_type

DART needs to know if the East-West domain is cyclic for spatial interpolations. Presently, DART has only been tested for the dipole grid, which is cyclic E-W and closed N-S.

Contents	Type	Description
ew_boundary_type	character(len=64)	switch to indicate whether the East-West domain is cyclic or not. DART/POP has not been tested in a regional configuration, so DART requires this to be `'cyclic'`. [default: ‘cyclic’]

namelist /grid_nml/  horiz_grid_opt,  vert_grid_opt,  topography_opt, &
                               horiz_grid_file, vert_grid_file, topography_file

The POP grid information comes in several files: horizontal grid lat/lons in one, the vertical grid spacing in another, and the topography (lowest valid vertical level) in a third.

Here is what we can get from the (binary) horizontal grid file:

real(r8), dimension(:,:) :: ULAT,  &! latitude  (radians) of U points
real(r8), dimension(:,:) :: ULON,  &! longitude (radians) of U points
real(r8), dimension(:,:) :: HTN ,  &! length (cm) of north edge of T box
real(r8), dimension(:,:) :: HTE ,  &! length (cm) of east  edge of T box
real(r8), dimension(:,:) :: HUS ,  &! length (cm) of south edge of U box
real(r8), dimension(:,:) :: HUW ,  &! length (cm) of west  edge of U box
real(r8), dimension(:,:) :: ANGLE  &! angle

The vertical grid file is ascii, with 3 columns/line:

cell thickness(in cm)   cell center(in m)   cell bottom(in m)

Here is what we can get from the topography file:

integer, dimension(:,:), :: KMT    &! k index of deepest grid cell on T grid

These must be derived or come from someplace else …

KMU               k index of deepest grid cell on U grid
HT                real(r8) value of deepest valid T depth (in cm)
HU                real(r8) value of deepest valid U depth (in cm)

Contents	Type	Description
horiz_grid_opt, vert_grid_opt, topography_opt	character(len=64)	switch to indicate whether or not the grids will come from an external file or not. DART requires ALL of these to be `'file'`. [default: ‘file’]
horiz_grid_file	character(len=100)	The name of the binary file containing the values for the horizontal grid. The dimensions of the grid are read from `pop.r.nc`. It would have been nice to include the actual grid information in the netCDF files. [default: ‘horiz_grid.gx3v5.r8ieee.le’]
vert_grid_file	character(len=100)	The name of the ASCII file containing the values for the vertical grid. The file must contain three columns of data pertaining to the cell thickness (in cm), the cell center (in meters), and the cell bottom (in meters). Again, it would have been nice to include the vertical grid information in the netCDF files. [default: ‘vert_grid.gx3v5’]
topography_grid_file	character(len=100)	The name of the binary file containing the values for the topography information. The dimensions of the grid are read from `pop.r.nc`. [default: ‘topography.gx3v5.r8ieee.le’]

Other modules used¶

types_mod
time_manager_mod
utilities_mod
typesizes
netcdf

Public interfaces¶

Only a select number of interfaces used are discussed here. Each module has its own discussion of their routines.

Interface routines¶

use dart_pop_mod, only :	get_pop_calendar
	set_model_time_step
	get_horiz_grid_dims
	get_vert_grid_dim
	read_horiz_grid
	read_topography
	read_vert_grid
	write_pop_namelist
	get_pop_restart_filename

Required interface routines¶

call get_pop_calendar(calstring)

character(len=*), intent(out) :: calstring

Returns a string containing the type of calendar in use.

calstring

DART/POP uses a ‘gregorian’ calendar.

poptimestep = set_model_time_step()

type(time_type), intent(out) :: poptimestep

set_model_time_step returns the model time step that was set in the restart_nmlrestart_freq. This is the minimum amount of time DART thinks the POP model can advance. Indirectly, this specifies the minimum assimilation interval.

poptimestep

the minimum assimilation interval

call get_horiz_grid_dims(Nx, Ny)

integer, intent(out) :: Nx, Ny

get_horiz_grid_dims reads pop.r.nc to determine the number of longitudes and latitudes.

`Nx`	the length of the ‘i’ dimension in the POP restart file. The number of longitudes in use.
`Ny`	the length of the ‘j’ dimension in the POP restart file. The number of latitudes in use.

call get_vert_grid_dim( Nz )

integer, intent(out) :: Nz

get_vert_grid_dim reads pop.r.nc to determine the number of vertical levels in use.

`Nz`	the length of the ‘k’ dimension in the POP restart file. The number of vertical levels in use.

call read_horiz_grid(nx, ny, ULAT, ULON, TLAT, TLON)

integer,                    intent(in)  :: nx, ny
real(r8), dimension(nx,ny), intent(out) :: ULAT, ULON, TLAT, TLON

read_horiz_grid reads the direct access binary files containing the POP grid information. The first record is REQUIRED to be ‘ULAT’, the second record is REQUIRED to be ‘ULON’.

`nx`	The number of longitudes in the grid.
`ny`	The number of latitudes in the grid.
`ULAT`	The matrix of latitudes for the UVEL and VVEL variables. Units are degrees [-90,90].
`ULON`	The matrix of longitudes for the UVEL and VVEL variables. Units are degrees. [0,360]
`TLAT`	The matrix of latitudes for the SALT and TEMP variables. Units are degrees [-90,90].
`TLON`	The matrix of longitudes for the SALT and TEMP variables. Units are degrees. [0,360]

call read_topography(nx, ny, KMT, KMU)

integer,                   intent(in)  :: nx, ny
integer, dimension(nx,ny), intent(out) :: KMT, KMU

read_topography reads the direct access binary files containing the POP topography information. The first record is REQUIRED to be ‘KMT’. ‘KMU’ is calculated from ‘KMT’.

`nx`	The number of longitudes in the grid.
`ny`	The number of latitudes in the grid.
`KMT`	The matrix containing the lowest valid depth index at grid centroids.
`KMU`	The matrix containing the lowest valid depth index at grid corners.

call read_vert_grid(nz, ZC, ZG)

integer,                 intent(in)  :: nz
real(r8), dimension(nz), intent(out) :: ZC, ZG

read_vert_grid reads the ASCII file containing the information about the vertical levels. The file must contain
three columns of data pertaining to; 1) the cell thickness (in cm),
2) the cell center (in meters),
and 3) the cell bottom (in meters).

`nz`	The number of vertical levels.
`ZC`	The depth (in meters) at the grid centers.
`ZG`	The depth (in meters) at the grid edges.

call write_pop_namelist(model_time, adv_to_time)

type(time_type), intent(in)  :: model_time
type(time_type), intent(in)  :: adv_to_time

write_pop_namelist writes the POP namelist time_manager_nml with the information necessary to advance POP to the next assimilation time. The namelist is written to a file called pop_in.DART. Presently, DART is configured to minimally advance POP for 86400 seconds - i.e. 1 day. The forecast length (the difference between ‘model_time’ and ‘adv_to_time’) must be an integer number of days with the current setup. An error will result if it is not.

`model_time`	The ‘valid’ time of the current model state.
`adv_to_time`	The time of the next assimilation.

call get_pop_restart_filename( filename )

character(len=*), intent(out) :: filename

get_pop_restart_filename returns the filename containing the POP restart information. At this point the filename is hardwired to pop.r.nc, but may become more flexible in future versions. The filename may be derived from the restart_nml but is currently ignored.

filename

The name of the POP restart file.

Files¶

filename	purpose
pop_in	to read the POP namelists
pop.r.nc	provides grid dimensions and ‘valid_time’ of the model state
`&grid_nml` “horiz_grid_file”	contains the values of the horizontal grid
`&grid_nml` “vert_grid_file”	contains the number and values of the vertical levels
`&grid_nml` “topography_grid_file”	contains the indices of the wet/dry cells
pop_in.DART	to control the integration of the POP model advance

References¶

none

Private components¶

N/A