Using MOM supergrid in CICE causes large numbers of velocity truncations

[dougiesquire]

Using MOM supergrid in CICE causes large numbers of velocity truncations. These occur within the first few timesteps and may indicate an issue (e.g. see ACCESS-NRI/access-om3-configs#173). We've decided to revert to using the old CICE grid while we investigate.

[anton-seaice]

I can look into this but it may not be this week - has anyone checked what happens with the 1degree configs?

( This is related to #101, implementing mom supergrid in cice gives exact match in grid between cice & mom)

[dougiesquire]

has anyone checked what happens with the 1degree configs

@anton-seaice I haven't - all I can say is that it does run without truncations for at least 1 day. Would you prefer to keep the CICE grid change out of this PR until you have time to investigate?

[anton-seaice]

Its quite possibly related to sea ice initial conditions being different in 0.25 degree - so lets leave it in 1deg+ryf for now. I am not sure what to do with 1deg+iaf/wombat which we haven't merged yet.

[dougiesquire]

Its quite possibly related to sea ice initial conditions being different in 0.25 degree - so lets leave it in 1deg+ryf for now. I am not sure what to do with 1deg+iaf/wombat which we haven't merged yet.

Okay ta. I'll also leave in 1deg+iaf/wombat then by the same argument (better initial conditions)

[dougiesquire]

Our 0.25 deg has a few changes that weren't propagated to the 1 deg configs, but should have been. I'm trying to get them up to date. One of those changes is to use the MOM parameter DIABATIC_FIRST = False (see #137). However, when I set this in the dev-1deg_jra55do_ryf configuration, the model crashes within the first few timesteps due to MOM velocity trunctions. If I revert the CICE supergrid changes, the model doesn't crash. This is demonstrated in this PR.

@anton-seaice, how do you feel about reverting the CICE supergrid changes in the 1deg configs as well until you've had some time to investigate? At the very least it would mean that all our configs are consistent.

[anton-seaice]

Yeah thats ok by me