PDAF_assimilate_lenkf

This page documents the routine PDAF_assimilate_enkf of PDAF. The routine is used to execute the analysis step of the localized EnKF.

The routine is typically called in assimilate_pdaf or directly in the model code. However, for newer implementations we recommend to use PDAFlocalomi_assimilate_lenkf since less user-supplied call-back routines are required with the PDAFlocalomi 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. When the 'flexible' implementation variant, the routines `PDAF_put_state_*' are used.

The interface when using the LEnKF is the following:

  SUBROUTINE PDAF_assimilate_lenkf(U_collect_state, U_distribute_state, U_init_dim_obs, &
                                 U_obs_op, U_init_obs, U_prepoststep, U_localize, &
                                 U_add_obs_err, U_init_obscovar, U_next_observation, status_pdaf)

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 basically 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.
• U_init_dim_obs: The name of the user-supplied routine that provides the size of 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_prepoststep: The name of the pre/poststep routine as in PDAF_get_state
• U_localize: The name of the routine that applied the covariance localization
• U_add_obs_err: The name of the user-supplied routine that adds the observation error covariance matrix to the ensemble covariance matrix projected onto the observation space.
• U_init_obscovar: The name of the user-supplied routine that initializes the observation error covariance matrix.
• U_next_observation: The name of a 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 PDAF_assimilate_lenkf is exited without errors.

The user-supplied call-back routines are described on the page on implementing the analysis step of the localized EnKF.

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