ctsm5.3.075: turn off LW downscaling over glacier elevation classes by default

[adamrher]

In tuning up the SMB over Greenland, @whlipscomb, @gunterl and I found that turning off the LW downscaling improves the melt and runoff biases, and would like it be the default in the CESM3 release. Specifically,

glcmec_downscale_longwave = .false.

as it currently defaults to true.

[adamrher]

(I currently don't have permissions to add labels, assignees, etc)

[ekluzek]

@adamrher I heard about this in the CSEG meeting. So I'm glad you made a ticket for it. We'll talk about it Thursday and figure out all the things regarding when and who then.

[ekluzek]

@whlipscomb @gunterl and @Katetc from above I'm assuming this is what you recommend as well?

In terms of CESM tags, right now this will come in with cesm3_0_alpha08a so part of the CESM beta tag after beta07 that's currently being worked on. The beta07 tag is still a few weeks out right now...

[whlipscomb]

@ekluzek: Yes, based on Adam's recent runs, we think this change will improve the Greenland SMB (less melt and less runoff, especially in the west and southeast where the biases relative to RACMO are largest). We're not aware of any down sides to the change.