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Overview of the Analysis Step of Ensemble Filters
PDAF-OMI Guide
- Overview
- callback_obs_pdafomi.F90
- Observation Modules
- Observation operators
- Checking error status
- Debugging functionality
- Implementing the analysis step with OMI
- General overview for ensemble filters
- General overview for 3D-Var methods
- Using nondiagonal R-matrices
- Porting an existing implemention to OMI
- Additional OMI Functionality
Implementation Guide
For the analysis step of ensemble filters several routines need to be implemented. We prove a conceptional overview here. The detailed interfaces are then described on the following pages.
Figure 1: Required routines for the analysis step of ensemble filters. There are three groups of routines: The interface to the model (orange), the observation module (red), and state localization in case of domain-localized filters like LETKF/LESTKF/LNETF (purple). Without PDAFlocal there are two additional routines in the localization module.
Figure 1 gives an overview of the different routines that might need to be provided to the analysis step of an ensemble filter. The actual routines depend on the chosen filter method. The routines are organized in three groups:
Model Interface
The model Interface consists of the routines
collect_state_pdaf
anddistribute_state_pdaf
. These routine perform the concersion between model fields and state vector. The routines have been discussed in the context of the modification of the model for the ensemble integration.
OMI Observation Module
The observation module performs all observation-related operations. In case of OMI, one needs the following routines:
init_dim_obs_pdafomi
: For each observation type that is assimilation this routine reads the observations and initialized observation values, coordinates, and errors. In addition indices are specified that link the state vector to the observations so that the observation operator is preparedobs_op_pdafomi
: For each observation type there is one routine providing the observation operator. For this, OMI provides different observation operatorsinit_dim_obs_l_pdafomi
: This routine initializes the local observations of each observation type. This is only required for the domain-localized filters. With OMI this is mainly a single subroutine call, while OMI does the actual initializationlocalized_covar
: For the local EnKF the state error covariance matrix is localized. This is performed with this routine and is specified for each observation type.
More information about OMI can be found in the overview of PDAF-OMI.
Localization
These routines are only required for the domain-localized ensemble filters. They handle the initialization of the state vector for a local analysis. These routines are
init_n_domain
: This routine sets the number of local analysis domainsinit_dim_l
: This routine determines the state vector size for the local analysis domain and initializes the index information to fill a local state vector
Code examples in tutorial
The implementation of the ensemble filters is demonstrated in the tutorial codes in the PDAF package in the sub-directories of
tutorial/
The implementations are described in detail in the PDAF tutorial slide sets.
Documention of the required implementations
There are three different routines that call the filter analysis step: