[MITgcm-devel] switching seaice_obcs from legacy to devel

[Menemenlis, Dimitris (3248)]

Dear MITgcm sea ice developers, as requested I am working on switching
verification/seaice_obcs from legacy to devel code.

With #undef SEAICE_GROWTH_LEGACY
I get some rather large differences in the output of the 3 experiments:

Y Y Y Y> 2< 2  7  5  5  5  9  7  4  1  1  2  2 16  2  3  2  0  2  0  0  0  4  3  3 FAIL  seaice_obcs
Y Y Y Y> 2< 2  7  5  4  5  9  7  4  1  1  3  2 16  1  3  2  0  2  0  0  0  3  3  3 FAIL  seaice_obcs.seaiceSponge
Y Y Y Y> 3< 2  7  5  5  5 10  7  4  2  1  3  3  1  3  3  3  0  2  0  0  0  4  3  3 FAIL  seaice_obcs.tides

I have traced this difference back to large differences in "AREA" between legacy and devel branches.
In attached figure I plot AREA, HEFF, and Qsw after 6 model time steps for the legacy
and devel branches an for the difference.
Note that in region of very thin ice (lower right quadrant of panels),
the legacy code gives ~100% ice cover, while the devel code give ~0% ice cover.
This has big consequence for shortwave radiation.

I have following questions:

- Do you know what is causing this difference?

- Are there compile-time or run-time flag options that can reduce this difference?

- Shall we just check in the new output.txt as is?
  For the things that are being tested in seaice_obcs, this difference is probably not important,
  and the devel treatment is probably more realistic in terms of shortwave forcing.

Dimitris Menemenlis

[cid:DBA91688-2D4A-49A1-A3EE-CF42DE4A36E1 at jpl.nasa.gov]
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