= PDAF_iau_reset = 

This page documents the routine `PDAF_iau_reset` of PDAF, which was introduced with PDAF V3.0.

This routine is used to modify the IAU type and the number of IAU time steps during a run. While [wiki:PDAF_iau_init `PDAF_iau_init`] sets the IAU type and number of IAU steps initially, one can change these settings during a model run. 

The routine has to be called by all processes that are model processes. A common place is to call the routine in `assimilate_pdaf` after an analysis step or in `distribute_state_pdaf`.

The interface is:
{{{
  SUBROUTINE PDAF_iau_reset(type_iau, nsteps_iau, flag)

    INTEGER, INTENT(in) :: type_iau     ! Type of IAU
                                        !   (0) no IAU
                                        !   (1) constant increment weight 1/nsteps_iau
                                        !   (2) Linear IAU weight with maximum in middle of IAU period
                                        !   (3) Zero weights for null mode (can be used to apply IAU on user side)
    INTEGER, INTENT(in) :: nsteps_iau   ! number of time steps in IAU
    INTEGER, INTENT(out) :: flag        ! Status flag

}}}

Hints:
 * It is recommended to only call this routine after or just before a forecast phase.
 * Calling this routine during a forecast phase will change the IAU weights and might stop the application of IAU if `nsteps_iau` is below the number of time steps performed in the current forecast phase.