Changes between Version 2 and Version 3 of ImplementAnalysislenkfOmi


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Timestamp:
Nov 24, 2020, 2:58:07 PM (3 months ago)
Author:
lnerger
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  • ImplementAnalysislenkfOmi

    v2 v3  
    2424[[PageOutline(2-3,Contents of this page)]]
    2525
    26 With Version 1.16 of PDAF we introduced PDAF-OMI (observation module infrastructure). With OMI, a smaller number of routines needs to be supplied by the user than in the previous implementation approach.
     26
    2727
    2828== Overview ==
    2929
    30 For the analysis step of the LEnKF different operations related to the observations are needed. These operations are requested by PDAF by calling user-supplied routines. Intentionally, the operations are split into separate routines in order to keep the operations rather elementary. This procedure should simplify the implementation. The names of the required routines are specified in the call to the routine `PDAFomi_put_state_lenkf` for the fully-parallel implementation (or `PDAFomi_put_state_lenkf` for the 'flexible' implementation). With regard to the parallelization, all these routines are executed by the filter processes (`filterpe=.true.`) only.
     30With Version 1.16 of PDAF we introduced PDAF-OMI (observation module infrastructure). With OMI, a smaller number of routines needs to be supplied by the user than in the previous implementation approach. This page described the implementation of the analysis step for the local EnKF (LEnKF).
     31
     32For the analysis step of the global filters we need different operations related to the observations. These operations are requested by PDAF by call-back routines supplied by the user and provided in the OMI structure. The names of the required routines are specified in the call to the routine `PDAFomi_put_state_lenkf` for the fully-parallel implementation (or `PDAFomi_put_state_lenkf` for the 'flexible' implementation). With regard to the parallelization, all these routines (except `U_collect_state`, `U_distribute_state`, and `U_next_observation`) are executed by the filter processes (`filterpe=.true.`) only.
    3133
    3234For completeness we discuss here all user-supplied routines that are specified in the interface to `PDAFomi_put_state_lenkf`. Thus, some of the user-supplied routines that are explained on the page explaining the modification of the model code for the ensemble integration are repeated here.
     
    3436The LEnKF implemented in PDAF follows the original LEnKF by Evensen (1994) including the correction for perturbed observations (Burgers et al. 1998). The LEnKF implemented in PDAF is reviewed by Nerger et al (2005) and described in more detail by Nerger (2004). The localization is covariance lozalization of PH^T and HPH^T as described in Houtekamer & Mitchell (2001) (See the [PublicationsandPresentations page on publications and presentations] for publications and presenations involving and about PDAF)
    3537
    36 In our studies (Nerger et al. 2005, Nerger et al. 2007), the EnKF showed performance deficiencies compared to the SEIK filter. Due to this, we focused more on the SEIK filter and the ETKF and ESTKF after these comparison studies. For real applications, we generally recommend using ESTKF or ETKF, or their local variants LESTKF or LETKF. However, the EnKF/LEnKF might have a good performance if very large ensemble can be used as this reduces the sampling errors.
     38In our studies (Nerger et al. 2005, Nerger et al. 2007), the EnKF showed performance deficiencies compared to the SEIK filter. Due to this, we focused more on the SEIK filter, the ETKF and the ESTKF after these comparison studies. For real applications, we generally recommend using ESTKF or ETKF, or their local variants LESTKF or LETKF. However, the EnKF/LEnKF might have a good performance if very large ensemble can be used as this reduces the sampling errors.
    3739
    3840== `PDAFomi_assimilate_lenkf` ==
    3941
    40 The general aspects of the filter specific routines `PDAF_assimilate_*` have been described on the page [ModifyModelforEnsembleIntegration Modification of the model code for the ensemble integration] and its sub-page on [InsertAnalysisStep inserting the analysis step]. The routine is used in the fully-parallel implementation variant of the data assimilation system. When the 'flexible' implementation variant is used, the routines `PDAF_put_state_*' is used as described further below. Here, we list once more the full interface of the routine. Subsequently, the full set of user-supplied routines specified in the call to `PDAFomi_assimilate_lenkf` is explained.
     42The general aspects of the filter specific routines `PDAF_assimilate_*` have been described on the page [ModifyModelforEnsembleIntegration Modification of the model code for the ensemble integration] and its sub-page on [InsertAnalysisStep inserting the analysis step]. The routine is used in the fully-parallel implementation variant of the data assimilation system. When the 'flexible' implementation variant is used, the routines `PDAF_put_state_*' is used as described further below. Here, we list the full interface of the routine. Subsequently, the user-supplied routines specified in the call is explained.
    4143
    4244The interface when using the LEnKF is the following:
    4345{{{
    4446  SUBROUTINE PDAFomi_assimilate_lenkf(U_collect_state, U_distribute_state, &
    45                                  U_init_dim_obs, U_obs_op, &
    46                                  U_prepoststep, U_localize_covar, &
     47                                 U_init_dim_obs_pdafomi, U_obs_op_pdafomi, &
     48                                 U_prepoststep, U_localize_covar_pdafomi, &
    4749                                 U_next_observation, status)
    4850}}}
     
    5052 * [#U_collect_statecollect_state_pdaf.F90 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.
    5153 * [#U_distribute_statedistribute_state_pdaf.F90 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.
    52  * [#U_init_dim_obscallback_obs_pdafomi.F90 U_init_dim_obs]: The name of the user-supplied routine that provides the size of observation vector
    53  * [#U_obs_opcallback_obs_pdafomi.F90 U_obs_op]: The name of the user-supplied routine that acts as the observation operator on some state vector
     54 * [#U_init_dim_obs_pdafomicallback_obs_pdafomi.F90 U_init_dim_obs_pdafomi]: The name of the user-supplied routine that initializes the observation information and provides the size of observation vector
     55 * [#U_obs_op_pdafomicallback_obs_pdafomi.F90 U_obs_op_pdafomi]: The name of the user-supplied routine that acts as the observation operator on some state vector
    5456 * [#U_prepoststepprepoststep_ens_pdaf.F90 U_prepoststep]: The name of the pre/poststep routine as in `PDAF_get_state`
    55  * [#U_localize_covarcallback_obs_pdafomi.F90 U_localize_covar]: Apply covariance localization to the matrices HP and HPH^T^
     57 * [#U_localize_covar_pdafomicallback_obs_pdafomi.F90 U_localize_covar]: Apply covariance localization to the matrices HP and HPH^T^
    5658 * [#U_next_observationnext_observation_pdaf.F90 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`.
    5759 * `status`: The integer status flag. It is zero, if `PDAFomi_assimilate_lenkf` is exited without errors.
     
    6466{{{
    6567  SUBROUTINE PDAFomi_put_state_lenkf(U_collect_state, &
    66                                  U_init_dim_obs, U_obs_op, &
    67                                  U_prepoststep, U_localize, &
     68                                 U_init_dim_obs_pdafomi, U_obs_op_pdafomi, &
     69                                 U_prepoststep, U_localize_covar_pdafomi, &
    6870                                 status)
    6971}}}
     
    7476Here all user-supplied routines are described that are required in the call to `PDAFomi_assimilate_lenkf`. For some of the generic routines, we link to the page on [ModifyModelforEnsembleIntegration modifying the model code for the ensemble integration].
    7577
    76 To indicate user-supplied routines we use the prefix `U_`. In the template directory `templates/` as well as in the example implementation in `testsuite/src/dummymodel_1D` these routines exist without the prefix, but with the extension `_pdaf.F90`. In the section titles below we provide the name of the template file in parentheses.
     78To indicate user-supplied routines we use the prefix `U_`. In the template directory `templates/` as well as in the example implementation in `testsuite/src/dummymodel_1D` these routines exist without the prefix, but with the extension `_pdaf.F90`. The user-routines relating to OMI are collected in the file `callback_obs_pdafomi.F90`. In the section titles below we provide the name of the template file in parentheses.
    7779
    7880In the subroutine interfaces some variables appear with the suffix `_p`. This suffix indicates that the variable is particular to a model sub-domain, if a domain decomposed model is used. Thus, the value(s) in the variable will be different for different model sub-domains.
     
    8284
    8385This routine is independent of the filter algorithm used.
     86
    8487See the page on [InsertAnalysisStep#U_collect_statecollect_state_pdaf.F90 inserting the analysis step] for the description of this routine.
    8588
     
    8891
    8992This routine is independent of the filter algorithm used.
     93
    9094See the page on [InsertAnalysisStep#U_distribute_statedistribute_state_pdaf.F90 inserting the analysis step] for the description of this routine.
    9195
    9296
    93 === `U_init_dim_obs` (callback_obs_pdafomi.F90) ===
     97=== `U_init_dim_obs_pdafomi` (callback_obs_pdafomi.F90) ===
    9498
    95 This routine is used by all global filter algorithms (SEEK, SEIK, EnKF, ETKF, NETF, PF) and by the LEnKF.
     99This is a call-back routine for PDAF-OMI initializing the observation information. The routine just calls a routine from the observation module for each observation type.
    96100
    97 The interface for this routine is:
    98 {{{
    99 SUBROUTINE init_dim_obs_pdafomi(step, dim_obs_p)
    100 
    101   INTEGER, INTENT(in)  :: step       ! Current time step
    102   INTEGER, INTENT(out) :: dim_obs_p  ! Dimension of observation vector
    103 }}}
    104 
    105 The routine is called at the beginning of each analysis step.  It has to initialize the size `dim_obs_p` of the observation vector according to the current time step. Without parallelization `dim_obs_p` will be the size for the full model domain. When a domain-decomposed model is used, `dim_obs_p` will be the size of the observation vector for the sub-domain of the calling process.
    106 
    107 With PDAF-OMI, the routine just calls a routine from the observation module for each observation type.
     101See the [wiki:OMI_Callback_obs_pdafomi documentation on callback_obs_pdafomi.F90] for more information.
    108102
    109103
    110 === `U_obs_op` (calllback_obs_pdafomi.F90) ===
    111104
    112 This routine is used by all global filter algorithms (SEEK, SEIK, EnKF, ETKF, NETF, PF) and the LEnKF.
     105=== `U_obs_op_pdafomi` (callback_obs_pdafomi.F90) ===
    113106
    114 The interface for this routine is:
    115 {{{
    116 SUBROUTINE obs_op_pdafomi(step, dim_p, dim_obs_p, state_p, m_state_p)
     107This is a call-back routine for PDAF-OMI applying the observation operator to the state vector. The routine calls a routine from the observation module for each observation type.
    117108
    118   INTEGER, INTENT(in) :: step               ! Currrent time step
    119   INTEGER, INTENT(in) :: dim_p              ! PE-local dimension of state
    120   INTEGER, INTENT(in) :: dim_obs_p          ! Dimension of observed state
    121   REAL, INTENT(in)    :: state_p(dim_p)     ! PE-local model state
    122   REAL, INTENT(out) :: m_state_p(dim_obs_p) ! PE-local observed state
    123 }}}
    124 
    125 The routine is called during the analysis step. It has to perform the operation of the observation operator acting on a state vector that is provided as `state_p`. The observed state has to be returned in `m_state_p`.
    126 
    127 For a model using domain decomposition, the operation is on the PE-local sub-domain of the model and has to provide the observed sub-state for the PE-local domain.
    128 
    129 With PDAF-OMI, the routine just calls a routine from the observation module for each observation type.
     109See the [wiki:OMI_Callback_obs_pdafomi documentation on callback_obs_pdafomi.F90] for more information.
    130110
    131111
    132112=== `U_prepoststep` (prepoststep_ens_pdaf.F90) ===
    133113
    134 The general aspects of this routines have already been described on the [ModifyModelforEnsembleIntegration#U_prepoststepprepoststep_ens_pdaf.F90 page on modifying the model code for the ensemble integration] for the SEIK filter. For completeness, the description is repeated specifically for the EnKF:
     114The routine has already been described for modifying the model for the ensemble integration and for inserting the analysis step.
    135115
    136 The interface of the routine is identical for all filters, but sizes can vary. Also, the particular operations that are performed in the routine can be specific for each filter algorithm.
    137 
    138 The interface for this routine is for the LEnKF
    139 {{{
    140 SUBROUTINE prepoststep(step, dim_p, dim_ens, dim_ens_p, dim_obs_p, &
    141                        state_p, Uinv, ens_p, flag)
    142 
    143   INTEGER, INTENT(in) :: step        ! Current time step
    144                          ! (When the routine is called before the analysis -step is provided.)
    145   INTEGER, INTENT(in) :: dim_p       ! PE-local state dimension
    146   INTEGER, INTENT(in) :: dim_ens     ! Size of state ensemble
    147   INTEGER, INTENT(in) :: dim_ens_p   ! PE-local size of ensemble
    148   INTEGER, INTENT(in) :: dim_obs_p   ! PE-local dimension of observation vector
    149   REAL, INTENT(inout) :: state_p(dim_p) ! PE-local forecast/analysis state
    150                                      ! The array 'state_p' is not generally not initialized in the case of SEIK/EnKF/ETKF.
    151                                      ! It can be used freely in this routine.
    152   REAL, INTENT(inout) :: Uinv(1, 1)  ! Not used not LEnKF
    153   REAL, INTENT(inout) :: ens_p(dim_p, dim_ens)      ! PE-local state ensemble
    154   INTEGER, INTENT(in) :: flag        ! PDAF status flag
    155 }}}
    156 
    157 The routine `U_prepoststep` is called once at the beginning of the assimilation process. In addition, it is called during the assimilation cycles before the analysis step and after the ensemble transformation. The routine is called by all filter processes (that is `filterpe=1`).
    158 
    159 The routine provides for the user the full access to the ensemble of model states. Thus, user-controlled pre- and post-step operations can be performed.  For example the forecast and the analysis states and ensemble covariance matrix can be analyzed, e.g. by computing the estimated variances. In addition, the estimates can be written to disk.
    160 
    161 Hint:
    162  * If a user considers to perform adjustments to the estimates (e.g. for balances), this routine is the right place for it.
    163  * Only for the SEEK filter the state vector (`state_p`) is initialized. For all other filters, the array is allocated, but it can be used freely during the execution of `U_prepoststep`.
    164  * The array `Uinv` is not used in the EnKF. Internally to PDAF, it is allocated to be of size (1,1).
    165  * Apart from the size of the array `Uinv`, the interface is identical for all ensemble filters (SEIK/ETKF/EnKF/LSEIK/LETKF/LEnKF). In general it should be possible to use an identical pre/poststep routine for all these filters.
    166  * The interface through which `U_prepoststep` is called does not include the array of smoothed ensembles. In order to access the smoother ensemble array one has to set a pointer to it using a call to the routine `PDAF_get_smootherens` (see page on [AuxiliaryRoutines auxiliary routines])
     116See the page on [InsertAnalysisStep#U_prepoststepprepoststep_ens_pdaf.F90 inserting the analysis step] for the description of this routine.
    167117
    168118
    169119
    170 === `U_localize` (callback_obs_pdafomi.F90) ===
     120=== `U_localize_covar_pdafomi` (callback_obs_pdafomi.F90) ===
    171121
    172122This routine is only used for the LEnKF.
     
    190140
    191141This routine is independent of the filter algorithm used.
     142
    192143See the page on [InsertAnalysisStep#U_next_observationnext_observation_pdaf.F90 inserting the analysis step] for the description of this routine.
    193144