PDAF_reset_forget

This page documents the routine PDAF_reset_forgt of PDAF. The routine was introduced with PDAF 2.0

The routine allows a user to reset the forgetting factor manually during the assimilation process. For the local ensemble Kalman filters the forgetting factor can be set either globally of differently for each local analysis domain. For the LNETF and the global filters only a global setting of the forgeting factor is possible. This routine allows users to set the forgetting factor case-specific. In addition, the implementation of adaptive choices for the forgetting factor (beyond what is implemented in PDAF) are possible.

The interface is the following:

  SUBROUTINE PDAF_reset_forget(forget)

with the following argument:

• forget: real, intent(in)
  The new value of the forgetting factor

How to use PDAF_reset_forget

• Global Filters and LNETF: For global filters PDAF_reset_forget has to be called before the actual analysis step. Within the PDAF context the call can be inserted in prepoststep_pdaf. Alternatively, the call can be inserted in the routine assimilation_pdaf before the call to the PDAF_assimilate_X or PDAF_put_state_X routines
• Local Filters:
  • global setting: The forgetting factor is reset globally, thus equal for all local analysis dimains, if PDAF_reset_forget is called before the local analysis loop is executed (e.g. in init_obs_pdomi or earlier in the analysis step; see [ImplementAnalysisLocal] for the order of the execution of the call-back routines). Thus, it can also be called in prepoststep_pdaf to get a global seeting as fo rthe global filters.
  • To reset forget specific for each local analysis domain, PDAF_reset_forget should be called during the local analysis loop. In particular the routines init_dim_l or init_dim_obs_l_pdafomi are suited for this.