PDAF3_assimilate_lenkf

This page documents the routine PDAF3_assimilate_lenkf of PDAF. The routine is part of the advanced PDAF3 interface that was introduced with PDAF V3.0.

Note: This routine exists for backward-compatibility for the LEnKF with PDAF V2.3, in particular for existing implementations using localize_covar_pdafomi. We recommend to use the new PDAF3 interface using PDAF3_assimilate_global that avoids the need to implement the additional call-back routine localize_covar_pdafomi.

The routine is used to execute the analysis step of the localized EnKF (LEnKF). The routine uses the functionalities provided by PDAF-OMI to yield a minimum number of arguments.

The routine is typically called in assimilate_pdaf or directly in the model code.

The general aspects of the filter specific routines PDAF3_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 both the fully-parallel and the flexible parallelization variant of the data assimilation system.

Here, we list the full interface of the routine.

The interface is:

  SUBROUTINE PDAF3_assimilate_lenkf(U_collect_state, U_distribute_state, &
                                 U_init_dim_obs_pdafomi, U_obs_op_pdafomi, &
                                 U_localize_covar_pdafomi, &
                                 U_prepoststep, U_next_observation, status)

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_pdafomi: The name of the user-supplied routine that initializes the observation information and provides the size of observation vector
• U_obs_op_pdafomi: The name of the user-supplied routine that acts as the observation operator on some state vector
• U_localize_covar_pdafomi: The name of the user-supplied routine that Applies covariance localization to the matrices HP and HPH^T
• U_prepoststep: The name of the user-supplied pre/poststep routine as in PDAF_get_state (Note that the place of U_prepoststep has changed compared to the previous routine PDAFomi_assimilate_lenkf)
• 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: The integer status flag. It is zero, if PDAFomi_assimilate_lenkf is exited without errors.

For the EnKF, the user-supplied routines are essentially executed in the order they are listed in the interface to PDAFomi_assimilate_lenkf.

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

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