Changes between Version 8 and Version 9 of ImplementationConceptOffline

Timestamp:

Feb 27, 2012, 12:09:33 PM (12 years ago)

Author:

lnerger

Comment:

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ImplementationConceptOffline

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+[[PageOutline(2-3,Contents of this page)]]
 
 In case of the offline mode of PDAF, the ensemble integrations are performed by the numerical model without required changes. After all ensemble members are integrated to the time when observations are to be assimilated, the assimilation program containing PDAF is started. The program reads the files from the model for all ensemble members. Subsequently, the analysis step of the chosen filter algorithm is computed. Finally, the updated ensemble states are written into input or restart files of the model. This completes the analysis step such that the next forecast phase can be computed.
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  * With the offline mode of PDAF, no direct coupling between PDAF and the model code is required. The exchange of information between the model and the assimilation program is performed solely through the output and restart files of the model. It requires that the user implements routines to read the model fields from the forecast files. In addition, routines are necessary that write the analysis state ensemble into restart files of the model. 
  * Model-specific operations like the initialization of the array of ensemble states in `PDAF_init` are actually performed by user-supplied routines. These routines are called through the standard interface of `PDAF`. Details on the interface and the required routines are given on the pages describing the implementation steps.
- * With regard to the parallelization, the assimilation program can be run on a single processor, i.e. without parallelization. The variables for the parallelization still have to be initialized by a call to `init_parallel_pdaf`. However, one does not need to compile with an MPI library, but it is sufficient to use the dummy implementation of the MPI-routines that is supplied with PDAF. If the model is parallelized, one need to ensure that the model fields are read correctly. In particular is in the parallel model each process write a separate files, one has to read these files sequentially in order to initialize an ensemble array holding the global state information.
+ * With regard to the parallelization, the assimilation program can be run on a single processor, i.e. without parallelization. The variables for the parallelization still have to be initialized by a call to `init_parallel_pdaf`. However, one does not need to compile with an MPI library, but it is sufficient to use the dummy implementation of the MPI-routines that is supplied with PDAF. If the model is parallelized, one needs to ensure that the model fields are read correctly. In particular, if in the parallel model each process writes a separate file, one has to read these files sequentially in order to initialize an ensemble array holding the global state information.
  * For large-scale models, it can be useful to execute the assimilation program with parallelization. Perhaps, following the domain decomposition of the model is the easiest strategy for this. In this case the decomposition information from the model has to be read into the assimilation program in order to initialize the state dimension of the sub-domains as well as the coordinates for each sub-domain.
  * The core routines of PDAF (those with the prefix `PDAF_`) are identical for the online and offline modes. The offline mode is switched on by selecting the corresponding subtype of the filter method in the call to `PDAF_init`.
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