ice_init: do broadcast 'default_season'

[phil-blain]

PR checklist

• Short (1 sentence) summary of your PR:
  title
• Developer(s):
  me
• Suggest PR reviewers from list in the column to the right.
• Please copy the PR test results link or provide a summary of testing completed below.
  Base suite is b4b with main on robert_intel:

349 measured results of 349 total results
349 of 349 tests PASSED
0 of 349 tests PENDING
0 of 349 tests MISSING data
0 of 349 tests FAILED

• How much do the PR code changes differ from the unmodified code?
  • bit for bit (since no test in the base suite change default_season)
  • different at roundoff level
  • more substantial if changing default_season
• Does this PR create or have dependencies on Icepack or any other models?
  • Yes
  • No
• Does this PR update the Icepack submodule? If so, the Icepack submodule must point to a hash on Icepack's main branch.
  • Yes
  • No
• Does this PR add any new test cases?
  • Yes
  • No
• Is the documentation being updated? ("Documentation" includes information on the wiki or in the .rst files from doc/source/, which are used to create the online technical docs at https://readthedocs.org/projects/cice-consortium-cice/. A test build of the technical docs will be performed as part of the PR testing.)
  • Yes
  • No, does the documentation need to be updated at a later time?
    • Yes
    • No
• Please provide any additional information or relevant details below:

When the 'default_season' namelist setting was added in 01494c7 (Nml settings (#208), 2018-10-19) to replace 'l_winter' and 'l_spring', a call to 'broadcast_scalar' was forgotten, such that the 'default_season' value from the namelist is only used on the first MPI process; all other processes get the hardcoded default value 'winter' defined in 'ice_init::input_data', resulting in different initialization across the grid for several variables if anything other than 'winter' is used in the namelist.

Fix that by broadcasting 'default_season' to all MPI procs.

[apcraig]

This is definitely a bug that could affect users if they set default_season to something other than the internal default. Just didn't affect any of our testing. Maybe we should try to fill that whole in the testing. default_season seems to set initial forcing values. Are they ever used and if so, under what conditions?

[eclare108213]

The default_season 'forcing' serves several purposes -- initialization of potentially missing forcing fields, simple values for short-period testing, and order-of magnitude guidance for users' own forcing fields. Thank you for fixing this bug, @phil-blain! @apcraig, if you want to add a test case for a different season, it could also test starting the code on a date other than Jan 1.

[phil-blain]

I can add a new test to this PR if we want to do that. I noticed that we do have tests with different default_season, but only in the Icepack base suite, not CICE's.