snow grain radius bug fix

[eclare108213]

• Short (1 sentence) summary of your PR:
  Fix snow radius limiting
• Developer(s):
  @eclare108213
• 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:
169 measured results of 169 total results
169 of 169 tests PASSED
0 of 169 tests PENDING
0 of 169 tests MISSING data
0 of 169 tests FAILED

• How much do the PR code changes differ from the unmodified code?
  • bit for bit in base_suite tests but I would expect the answers to change at some point
  • different at roundoff level
  • likely more substantial at times, but not expected to be climate-changing
• Does this PR create or have dependencies on CICE or any other models?
  • 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/.)
  • 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 snow metamorphism is active (snwgrain=.true.), the snow grain radius takes the tracer value (rsnow) but is limited by imposed minimum and maximum snow grain radius parameters. The minimum is the value assigned for freshly-fallen snow. The current code only limits the value above, not below. I expect this change to be non-BFB in runs with snow metamorphism; the current tests may not be long enough or otherwise configured to activate the limiting.

This is a single character modification! It was identified during the Icepack-merge-into-E3SM project.

[njeffery]

Approved by inspection.

[njeffery]

@eclare108213 : is this bug also in mpas-seaice?

[eclare108213]

No, it's not in MPAS-SI. It's one of the differences that Adrian noted.