Checking your initial assimilation

You may require several attempts to get your assimilation configured correctly. The next section, Computing filter increments, describes how to take the difference between two assimilation stages to determine whether your initial assimilation worked as intented.

If your assimilation does not change anything in the model state, you may need to rerun filter multiple times to understand what is wrong.

Thus you should make filter very fast to run. You can do this by:

Making an observation sequence file containing a single observation.
Configuring your run so that filter does a single assimilation and exits without having to advance the ensemble of models or do other work.

Making an observation sequence file containing a single observation

You can use one of these methods to make an obs_seq with just a single observation:

Run create_obs_sequence to make a new, short, observation sequence file.
Use the obs_sequence_tool to cut an existing obs_seq.out file down to just a few obs by selecting only a subset of the types and setting a very short time window, such as a second or two when you know there are observations available.

These programs are described in the Programs directory.

Configuring your run so that filter does a single assimilation and exits

To configure filter to only do a single assimilation:

Edit the &filter_nml namelist in input.nml to set the init_time_days and init_time_seconds to match the observation time in your truncated observation sequence file. This overrides any times in the input files and ensures that filter will only assimilate and not try to advance the model.
Make sure the truncated observation sequence file contains only a single observation or observations close enough together in time to fit into a single assimilation window.