prevent hang by erroring out if shortest_time_between_assimilations <=0

[hkershaw-brown]

Description:

Catch and error out when shortest_time_between_assimilations/get_model_time_step == 0
This prevents hangs in lower order models (e.g. lorenz_96) and "Inconsistent model state/observation times, cannot continue" in large models.

Note the routine shortest_time_between_assimilations and get_model_time_step are the same routine.

DART/assimilation_code/modules/assimilation/assim_model_mod.f90

Line 23 in 75cf8dc

get_model_time_step => shortest_time_between_assimilations, &

Fixes issue

fixes #535

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Documentation changes needed?

• My change requires a change to the documentation.
  • I have updated the documentation accordingly.

Tests

Please describe any tests you ran to verify your changes.

lorenz_96 with

&model_nml
   ...
   time_step_days    = 0,
   time_step_seconds = 0,
   /

hangs on main, errors out with message 'shortest_time_between_assimilations must be > 0' with this fix.

wrf with

&model_nml
   assimilation_period_seconds = 0,

Errors out with message 'shortest_time_between_assimilations must be > 0' with this fix

Checklist for merging

• Updated changelog entry
• Documentation updated
• Update conf.py

Checklist for release

• Merge into main
• Create release from the main branch with appropriate tag
• Delete feature-branch

Testing Datasets

• Dataset needed for testing available upon request
• Dataset download instructions included
• No dataset needed

[mjs2369]

Nice fix

Tried it with lorenz_96: code hangs on the main branch as expected, but errors out correctly with this check implemented

[braczka]

I would like to take a look at this soon, but just bogged down with other bugs -- go ahead and merge if you want to push this through though.