Create mushy macroscale drainage timescale parameter

[eclare108213]

• [x] Short (1 sentence) summary of your PR: Define a new parameter that sets the timescale (in days) for macroscopic drainage when using mushy thermodynamics. Fix some other documentation issues.
• [x] Developer(s): @eclare108213
• [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.

178 measured results of 178 total results 178 of 178 tests PASSED 0 of 178 tests PENDING 0 of 178 tests MISSING data 0 of 178 tests FAILED

• 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 CICE or any other models?

  • [ ] 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/.)

  • [x] Yes
  • [ ] No, does the documentation need to be updated at a later time?
    • [ ] Yes
    • [ ] No

• [x] Please provide any additional information or relevant details below:

• Define new parameter, tscale_pnd_drain, that sets the timescale (in days) for macroscopic drainage when using mushy thermodynamics. This parameterization is described in Turner and Hunke 2015 (eqn 47). It contributes to flushing along with gravity drainage, and therefore is not the timescale for flushing overall. tscale_pnd_drain = 1 / lambda_pond in icepack_therm_mushy.F90.

• Note: tscale_pnd_drain is not (yet) a namelist parameter, but it is now available in parameters for drivers to set their own values. This is needed for E3SM.

• Change the default value of dpscale (scaling factor for meltpond flushing with BL99 thermo) to 1.e-3 in the code. This is the value used in icepack_in and all of our tests.

• Clarify definition of dpscale in the code and documentation - dpscale alters the timescale for drainage but is only a unitless scaling factor.

• Fix enthalpy units in code comments. Closes #455 (CICE does not suffer from this issue).

[apcraig]

Do we need to test and merge quickly and get this onto the E3SM Icepack branch?

Do you want me to do any testing on cheyenne or are you comfortable from your testing everything is bit-for-bit and working? That looks OK to me, but happy to do more.

[eclare108213]

Yes, quickly please. It would be great if you can launch a quick test on cheyenne, but I don't expect any issues with these changes.

[apcraig]

I just fired up a test suite on cheyenne. Will approve and merge the PR after that, then create a PR back to E3SM Icepack cice-consortium/E3SM-icepack-initial-integration that @eclare108213 can merge there.