Use data glc model where we used to use CISM2%NOEVOLVE

[billsacks]

In compsets that currently use CISM2%NOEVOLVE – and will soon change to use SGLC – we'd like to instead use a data glc model in a time-constant mode. This should provide all of the benefits that we currently get from CISM2%NOEVOLVE: dictating glacier area and topographic heights over the ice sheet domain and providing a high-resolution grid onto which SMB and other fields can be downscaled.

We plan to develop this data glc model in CDEPS, which relies on NUOPC. So we will wait to make this switch until we are using NUOPC as a standard mode of operation (footnote this has happened now).

Definition of done:

• Update CISM and CTSM to use GLC_USE_ANTARCTICA Fixing Negative Ice Fluxes from Ocean to Glacier #2222
• Update CTSM with a version of CDEPS that supports DGLC (Make a data glc model CDEPS#25) and (Add a dglc component with noevolve mode CDEPS#268)
• Update to a DGLC Verision that handles negative runoff for glaciers
• Add I compsets to CTSM that exercise DGLC
• Add testing to CTSM that test needed DGLC cases
• Change most I compsets/tests to use DGLC rather than SGLC

[billsacks]

Blocked: depends on ESCOMP/CDEPS#25

[ekluzek]

LIWG is going to support a DGLC model rather than CISM%NOEVOLVE mode for CESM3. This means rather than fixing #2222 for CISM/CTSM the ability to run cases with DGLC will be setup. This is important for fully coupled compsets so that negative runoff is NOT sent to the ocean model. It looks right now the only CISM%NOEVOLVE compsets and tests are B1850 cases. So minimally we would only need to have a few tests around DGLC for 1850 with Bgc-Crop.

I added some notes about what needs to happen to the introduction for a "Definition of Done" above.

[billsacks]

@ekluzek - responding to and clarifying some points:

• The current implementation of dglc does not yet deal with the negative runoff issue. That is going to involve some substantial development, but yes, I think the current tentative plan is now to do that development in dglc rather than CTSM.
• Regarding which I compsets should be changed to use DGLC in NOEVOLVE mode: Others in the LIWG can comment on this as well, but my understanding is that nearly all I compsets (as well as F & B compsets) will be changed to use DGLC in NOEVOLVE mode; the main exception would be single-point / regional cases. This would go back to being more like how things were when I opened this issue a few years ago, when nearly all configurations used CISM%NOEVOLVE. We stopped using CISM%NOEVOLVE because it was becoming a support burden, but the plan at that time (and still now, I believe) is for these CISM%NOEVOLVE configurations to all be replaced with DGLC.
• The reasons it's better to run with DGLC over SGLC are: (a) this will ensure that glacier cover over Greenland and Antarctica agree with CISM's datasets (without requiring potentially frequent updates to CTSM's glacier raw dataset for this purpose); (b) this allows for downscaling of CTSM's surface mass balance to a high resolution glacier grid; and (c) this will allow for consistent treatment of runoff in various configurations, once this is enabled in DGLC (which isn't critical for an I compset, but it seems good to keep things consistent in this respect, and will allow testing this code in an I compset).

[ekluzek]

@billsacks and @Katetc I think this is something that's required for the June/30th science capability/functionality freeze correct? If so I'll mark it that way.

[wwieder]

Is this required for the summer science capability freeze or before the CESM3.0 release?