Add sea-ice variables to CORDEX-CMIP6 data request

[vmaurerDWD]

To be able to publish model output of coupled ocean-atmosphere models using a sea-ice component (which all ocean components running in the North and Baltic Seas usually possess) in one go, we need to add ocean variables (see #33 ) and sea-ice variables.

[vmaurerDWD]

Dear all (@HaHagemann, @sven-karsten, @WibkeDuesterhoeft),
we agreed to also include the sea-ice albedo. However, there is no such variable in the CMIP6 data request:

https://github.com/PCMDI/cmip6-cmor-tables/blob/main/Tables/CMIP6_SImon.json

Only the standard name sea_ice_albedo does exist.

If we want to add it, we need to define additional fields. What's your opinion on that?

[vmaurerDWD]

There are some further points which are not clear to me:

siconc has dimensions = longitude latitude time typesi -> what is typesi ? My guess is that this refers to the sea-ice categories? But I cannot really find where it is defined.

cell_methods : siconc and sivol have time: mean while sithick, sitemptop have time: mean where sea_ice (comment: mask=siconc) in the CMIP6 data request. I guess we should try keep it in line with CMIP6? But then we have to be careful that our model output is consistent.

[vmaurerDWD]

@sol1105 FYI

[larsbuntemeyer]

Thanks @vmaurerDWD for taking care.

siconc has dimensions = longitude latitude time typesi -> what is typesi ? My guess is that this refers to the sea-ice categories? But I cannot really find where it is defined.

The typesi dimesions refers to the sea ice area type dimension coordinate. We can add that to the coordinates table (it's created when the cmor tables are updated).

[jesusff]

For completeness, the sea_ice area type is defined here.

Is the plan to include all CMIP6 SImon variables? Even if these are "cheap" monthly variables, I would keep the data request to a moderate amount of variables, considering whether most models with sea-ice component will be able to provide these variables and whether the variables will actually be used in the future.

I ping also @PriscillaMooney from polar CORDEX, as they are likely to already have a data request for sea ice in those domains

[vmaurerDWD]

Thank you Lars and Chus for the clarification about typesi.

@jesusff : It was the plan initially to include all variables from CMIP6 SImon, but then we thought that we should start with this minimal list

https://github.com/WCRP-CORDEX/data-request-table/pull/54/files

and if other groups might want to add other sea-ice variables, they can still do it later. Or would you suggest a different procedure?

We also agreed with @sam-somot to discuss / circulate the issue at one point in the ocean task force.

[jesusff]

Thanks. I missed the PR. Looks good

[larsbuntemeyer]

@vmaurerDWD

cell_methods : siconc and sivol have time: mean while sithick, sitemptop have time: mean where sea_ice (comment: mask=siconc) in the CMIP6 data request. I guess we should try keep it in line with CMIP6? But then we have to be careful that our model output is consistent.

This is an MPI-ESM example. The difference is, in fact, that the, e.g., sea ice are fraction siconc should be masked with the ocean grid (where sea) while the actual sea ice thickness should only have values where there is acutally sea ice (where sea_ice). In other words: If there is no sea ice, it should be nan and not 0...