PDAF_prepost

This page documents the routine PDAF_prepost of PDAF.

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

The routine PDAF_prepost is an alternative to the routines PDAF_assimilate_X where 'X' is the name of a filter method. The routine can be used with the 'fully parallel' implementation variant of PDAF. The purpose of PDAF_prepost is to collect the ensemble information on the processes usually doing the filter analysis. However, in the case of PDAF_prepost, no filter analysis step is performed when the ensemble integration is complete, but only the user-supplied pre/poststep routine is called to allow the user to analyze the forecast ensemble.

The general aspects of the filter specific routines PDAF_assimilate_X are described on the page Modification of the model code for the ensemble integration and its sub-page on inserting the analysis step. For the 'flexible' implementation variant the alternative routine PDAF_put_state_prepost is used.

The interface is the following:

  SUBROUTINE PDAF_prepost(U_collect_state, U_distribute_state, U_prepoststep, &
                                 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_prepoststep: The name of the pre/poststep routine as in PDAF_get_state
• 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_prepoststep is exited without errors.

The user-supplied call-back routines are, for example, described on the page on implementing the analysis step of the ESKTF algorithm.

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

PDAF also has a Simplified Interface providing the routine PDAF_prepost_si. In the simplified interface, the name of the user-supplied routines have predefined names and do not appear in the call to PDAF_prepost_si. More information on the pre-defined names is provided, e.g., in the page on implementing the analysis step of the ESTKF algorithm.