Required model_mod routines

There are 18 Fortran subroutines required to interface a model with DART. Place these routines in your model_mod.f90 within DART/models/{your_model}. Many routines have sensible defaults in default_model_mod. For example, to use the default pert_model_copies routine add the following line in your model_mod.f90:

use default_model_mod, only : pert_model_copies

As in all Fortran programs, multiple routines can be listed after the colon.

Important

Always use the only keyword to import just the routines you need from default_model_mod.

Most models will still require custom implementations for some or all routines. The table below lists all 18 routines and their defaults. See Suggestions for a “simple” model (advanced by DART) or Suggestions for a “complex” model (advanced externally) for guidance.

Required model_mod routines

Routine	Purpose	Default behavior
init_time	Set the initial time if not read from the restart file.	Sets the initial time to 0 days, 0 seconds. To fail use init_time => fail_init_time.
init_conditions	For a “cold start” fill in an empty state vector with initial conditions. Many models cannot just make up values from thin air and thus choose to fail when this is requested.	Sets the initial state to 0. To fail use init_conditions => fail_init_conditions.
get_model_size	Return the number of items in the state vector.	Returns 1; i.e. there is only one item in the state.
static_init_model	Initialize DART with information about the model that will be used by the remaining model_mod routines. The procedure for doing this will depend on how complex the model is.	Does nothing.
get_state_meta_data	Takes an index into the state vector and returns the location corresponding to that value and optionally the variable quantity.	Sets a missing location and the default variable quantity.
end_model	Deallocate any arrays allocated in static_init_model.	Does nothing.
adv_1step	If possible, advance the model state from one time to another. Complex models will be unable to implement this method and should fail.	Call the error handler with the message “unable to advance model”.
shortest_time_ between_assimilations	Return a namelist or a fixed value for the minimum model advance time between assimilations. Note that complex models will handle advancing the time externally.	Returns a time period of 1 day.
model_interpolate	Interpolate a requested quantity to the given location to get an array of expected values for all ensemble members. NOTE: this is often the most time consuming method to implement.	Fail and set the expected observation to “missing.”
nc_write_model_atts	Add any additional information to the netCDF output diagnostic files. NOTE: the state will already be output by other routines, so this method should not create or write the state variables.	Does nothing.
read_model_time	Read the model time from a netCDF file.	Attempt to read the “time” variable from a state file in an intelligent way.
write_model_time	Write the model time to a netCDF file.	Write the “time” variable from the file according to the DART calendar.
pert_model_copies	Perturb a state vector in order to create an ensemble.	Add Gaussian noise with a specified amplitude to all parts of the state vector.
convert_vertical_obs	Some 3D models have multiple vertical coordinates (e.g. pressure, height, or model level); this method converts observations between different vertical coordinate systems.	Do no conversion.
convert_vertical_state	Some 3D models have multiple vertical coordinates (e.g. pressure, height, or model level); this method converts state between different vertical coordinate systems.	Do no conversion.
get_close_obs	Calculate which observations are “close” to a given location and, optionally, the distance. This is used for localization to reduce sampling error.	Uses the default behavior for determining distance.
get_close_state	Calculate which state points are “close” to a given location and, optionally, the distance. This is used for localization to reduce sampling error.	Uses the default behavior for determining distance.
nc_write_model_vars	This method is not currently called, so just use the default routine.	Does nothing.