Add a new diagnostic variable dvsdtd.

[dabail10]

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PR checklist

• [X] Short (1 sentence) summary of your PR: This adds a new diagnostic variable dvsdtd so that the SIMIP variable sndmassdyn can be used.
• [X] Developer(s): dabail10 (D. Bailey)
• [X] Suggest PR reviewers from list in the column to the right.
• [X] Please copy the PR test results link or provide a summary of testing completed below. https://github.com/CICE-Consortium/Test-Results/wiki/cice_by_hash_forks#1db0d9c13c0885c2da5c498a3fee0daa60788434
• How much do the PR code changes differ from the unmodified code?
  • [X] bit for bit
  • [ ] different at roundoff level
  • [ ] more substantial
• Does this PR create or have dependencies on Icepack or any other models?
  • [ ] Yes
  • [X] No
• Does this PR update the Icepack submodule? If so, the Icepack submodule must point to a hash on Icepack's main branch.
  • [ ] Yes
  • [X] No
• Does this PR add any new test cases?
  • [ ] Yes
  • [X] 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
  • [X] No, does the documentation need to be updated at a later time?
    • [ ] Yes
    • [X] No
• [X] Please document the changes in detail, including why the changes are made. This will become part of the PR commit log. We finally added the SIMIP variable sndmassdyn. This required the computation of dvsdtd. Also, there were some unit issues with some of the sndmass variables.

[apcraig]

Looks good. Is there not also a dvsdtt? These changes will need to be made to all of the drivers, eventually.

Since update_state is not backwards compatible, could you update all the call to update_state in all the other drivers. I would NOT add dvsdtd to those calls, but just update the arguments to use keywords= syntax. That should be adequate. Thanks.

[dabail10]

Ah. Good point. I will do that. I will also work on dvsdtt at the same time.

[dabail10]

I have added dvsdtt and fixed all of the calls to update_state in the drivers. The updated test results for the standalone driver are here:

https://github.com/CICE-Consortium/Test-Results/wiki/cice_by_hash_forks#e68dd144aa1577111f5a87f93378afd15847b62e

[apcraig]

I ran a test suite on Derecho and this all looks good. @dabail10, anything left to do? Any other comments? If not, I'll merge in the next day or two.

[dabail10]

I believe this is everything here.