Bug-fix: Mom6 time

[hkershaw-brown]

Description:

This pull request fixes read_model_time MOM6:

• MOM6 time is in days from year 1. DART time is from 1601. This pull request converts MOM6 time to DART time in read_model_time.

• Documentation updated to show how to turn on leap years for CESM (the default is no leap year). Added an example in the docs to illustrate Time in days vs. YYYY-MM-DD when you do not have leap years.

• The write_model_time is not converted back to MOM6 time. See MOM6 time  #494 for discussion on this. DART created files have dart time to match the observation times.

Fixes issue

fixes #494

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.

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]

Documentation is good! Are there other models in CESM that need this info added to their documentation pages? For example, I looked through the CLM documentation, and it doesn't talk about the calendar.

[hkershaw-brown]

The dart shell scripts for CLM, POP, CAM set the CALENDAR.

DART/models/clm/shell_scripts/cesm2_2/CLM5_setup_assimilation

Line 128 in 1b76f3a

./xmlchange CALENDAR=GREGORIAN

MOM6 with dart is fairly new (e.g. Robin developing the MOM6-Marble, Alper adding MOM6 multi-instance capability) so I figured it is worth noting in the docs about the calendar.

Maybe it is worth noting about the calendar in the CESM page? @kdraeder what do you think? https://docs.dart.ucar.edu/en/latest/models/CESM/readme.html

[mjs2369]

@hkershaw-brown we could move this discussion to email so that we can get this PR approved and released. Especially since the doc changes proposed above could be done in a separate PR. What do you think?

[hkershaw-brown]

@mjs2369 sounds like a plan, lets get this one out.