PDAF_assimilate_ensrf

This page documents the routine PDAF_assimilate_ensrf of PDAF. The routine is used to execute the ENSRF/EAKF filters, which was added to PDAF with version 3.0.

The routine is typically called in assimilate_pdaf or directly in the model code. However, for newer implementations we recommend to use the generic routine PDAF3_assimilate_local since less user-supplied call-back routines are required with the PDAF3 interface.

The general aspects of the filter specific routines PDAF_assimilate_* are described on the page Modification of the model code for the ensemble integration and its sub-page on inserting the analysis step. The routine is used in the fully-parallel implementation variant of the data assimilation system and can also be used for the flexible parallelization variant.

The interface for the ENSRF/EAKF is the following:

SUBROUTINE PDAF_assimilate_ensrf(U_collect_state, U_distribute_state, &
     U_init_dim_obs, U_obs_op, U_init_obs, U_init_obsvars, &
     U_localize_covar_serial, &
     U_prepoststep, U_next_observation, outflag)

with the following arguments:

• U_collect_state:
  The name of the user-supplied routine that initializes a state vector from the array holding the ensemble of model states from the model fields. This is the inverse operation to U_distribute_state used in PDAF_get_state as well as here.
• U_distribute_state:
  The name of a user supplied routine that initializes the model fields from the array holding the ensemble of model state vectors. This is the inverse operation to U_collect_state
• U_init_dim_obs:
  The name of the user-supplied routine that provides the size of the observation vector
• U_obs_op:
  The name of the user-supplied routine that acts as the observation operator on some state vector
• U_init_obs:
  The name of the user-supplied routine that initializes the vector of observations
• U_init_obsvars:
  The name of the user-supplied routine that initializes the vector of observation error variances.
• U_localize_covar_serial:
  The name of the user-supplied routine that applies the covariance localization for a single observation
• U_prepoststep:
  The name of the user-supplied pre/poststep routine as in PDAF_get_state
• U_next_observation:
  The name of the user-supplied routine that initializes the variables nsteps, timenow, and doexit. The same routine is also used in PDAF_get_state.
• status_pdaf:
  The integer status flag. It is zero, if the routine is exited without errors.

The user-supplied call-back routines are described on the page on implementing the analysis step of the ENSRF/EAKF. Here also the possible choices of subtype are explained. These select the particular filter variant.

It is recommended to check value of status_pdaf in the program after PDAF_assimilate_enkf is executed. Only if its value is 0 the initialization was successful.