Standard name: *New variable - solid-Earth model VILMA*

[SwatiGehlot]

The below proposed is a new standard name variable (relative sea level change) as a part of solid earth model VILMA, developed within the German paleo-climate initiative, Project PalMod (www.palmod.de)

Proposer's name: Swati Gehlot, DKRZ, Hamburg (technical description via Clemens Schannwell - clemens.schannwell@mpimet.mpg.de)

Date 2024-05-07

1. Relative sea-level change

Term: relative_sea_level_change Description: The change in local mean sea level relative to the local solid surface, i.e. sea floor Units: m CMOR name: rslc

[github-actions[bot]]

Thank you for your proposal. These terms will be added to the cfeditor (http://cfeditor.ceda.ac.uk/proposals/1) shortly. Your proposal will then be reviewed and commented on by the community and Standard Names moderator.

[JonathanGregory]

That's a good quantity to have in the standard name table, thanks. I won't disagree with the definition from https://doi.org/10.1007/s10712-019-09525-z! :smile:

[efisher008]

Hello Swati,

Thank you for your proposal, I have added the term to the CF editor. I agree that this would be a very relevant addition to the standard names table. There is an existing name global_average_sea_level_change, but this term's meaning is clearly distinct as it is a local quantity.

Perhaps the acronym RSLC for this term could be specified in the description, given it is used in the Gregory et al. 2019 paper mentioned by @JonathanGregory? There is accompanying text in the paper for the term, "Relative sea-level change is also called “relative sea-level rise” (RSLR)". This might also be useful to include in the description (would this be a good candidate for an alias @JonathanGregory?).

Would you suggest adding your colleague Clemens as a proposal author?

Best regards, Ellie

[efisher008]

Another question for @JonathanGregory,

I have found a set of names in the current standard name table with related descriptions: global_average_steric_sea_level_change global_average_thermosteric_sea_level_change

steric_change_in_mean_sea_level thermosteric_change_in_mean_sea_level halosteric_change_in_mean_sea_level

As far as I can tell, the global_average names are distinct from the mean_sea_level names in a similar way to the name in this proposal (i.e. the mean_sea_level names refer to a local relative change?). If this is the case, should the new name proposed by @SwatiGehlot follow the format relative_change_in_mean_sea_level, with its global "counterpart" being global_average_sea_level_change?

There is also a thermosteric_change_in_mean_sea_level but no global_average_halosteric_sea_level_change - perhaps there was not a need for this name in the original proposal, but should it be added for consistency?

Best, Ellie

[JonathanGregory]

Dear Ellie @efisher008

Thanks for your investigation. Coincidentally, I have been intending to review the sea level standard names, because of the anticipated needs of CMIP7. Firstly, I would like to propose that we change global_average to global_mean in all the relevant names, using aliases:

amplitude_of_global_average_sea_level_change global_average_sea_level_change global_average_steric_sea_level_change global_average_thermosteric_sea_level_change phase_of_global_average_sea_level_change tendency_of_global_average_sea_level_change

and the new one proposed by Aurore @abiardeau, where we have agreed on global_average_sea_level_change_due_to_change_in_ocean_mass. "Global average" is not wrong; it's synonymous with "global mean". However, "global mean" is much more common, and since it would be good to use the terminology of the AR6 I think it would be sensible to change.

You are absolutely correct that global_mean_sea_level_change is the global mean of relative sea level change, the term requested by @SwatiGehlot in this issue. The two terms don't quite correspond because there is no meaningful "global mean" of "mean sea level", and "relative sea level" (without "change") is also meaningless. "Relative sea level change" is the term commonly in use, but it's not obvious what "relative" means, namely that it's relative to the solid surface. This qualifier distinguishes it from geocentric sea level change, which is relative to the terrestrial reference frame. We haven't yet been asked for a standard name for geocentric SLC, but I think we should have one, since we should be asked for it! It's the quantity measured by satellite altimeters. For this, I would propose mean_sea_level_change_wrt_reference_ellipsoid, since reference_ellipsoid appears in other standard names.

Relative sea level change is the sum of steric_change_in_mean_sea_level and manometric sea level change, for which I would like to propose manometric_change_in_mean_sea_level. That's due to the change in the local mass per unit area of the ocean. steric_change_in_mean_sea_level is the sum of thermosteric_change_in_mean_sea_level and halosteric_change_in_mean_sea_level.

As you remarked, global_mean_thermosteric_sea_level_change is the global mean of thermosteric_change_in_mean_sea_level. There is no term for the global mean of halosteric_change_in_mean_sea_level because it's practically zero (see Appendix 2 of the paper, Why we can ignore global halosteric sea-level change). Some papers have evaluated it as a substantial quantity, but my understanding is that this is erroneous. Therefore global_mean_thermosteric_sea_level_change is practically equal to global_mean_steric_sea_level_change. Barystatic sea level change is the global counterpart of manometric sea level change, though not exactly the global mean.

All the above is context, and not directly relevant to the present issue. I should open a new issue for these points, but I thought it might be helpful here, given your question. The issue at hand is the standard name for "relative sea level change". To be self-explanatory, in CF style, we could give it the standard name mean_sea_level_change_wrt_sea_floor, since sea_floor is used in other standard names, or mean_sea_level_change_wrt_solid_surface if that is clearer. Swati said both in the proposal above, and we have both in the sea level concepts paper. What do you, @SwatiGehlot and any one else interested think? We should say in the definition that it's often called "relative sea level change" or "relative sea level rise".

Best wishes

Jonathan

[ClemensSchannwell]

Hi everyone,

as scientist behind this proposal, I thought I add my two cents here. I think, I would prefer @JonathanGregory's second suggestion mean_sea_level_change_wrt_solid_surface. The reason for this is that relative sea-level change also happens on land where the term „sea floor“ may be confusing. I like the idea about adding that it is commonly referred to as „relative sea-level change“ as this encompasses both sea-level rise and sea-level drop scenarios. I am less convinced about „relative sea level rise“ as this has a clear sign indication. I am also wondering, if we should add in the definition that the solid surface is with respect to some reference state, which could be present-day, but does not necessarily have to be.

Best wishes,

Clemens

[JonathanGregory]

Dear @ClemensSchannwell

Thanks for your helpful comment. You've raised two salient points:

• "Relative sea level rise has a clear sign indication." This remark makes me realise that all our "sea level change" standard names lack an indication of their sign convention. We try to ensure that the sign convention is explicit, when relevant, in CF standard names. It suggests to me that we should change them all to "sea level rise", and say in the description that a positive number means a rise in sea level, a negative number a fall in sea level. I'm pretty sure that "global-mean sea-level rise" is a commoner term than "global-mean sea-level change", though I'm not sure whether "relative sea level rise" is more or less common than "relative sea level change".

• The essential point about relative sea level rise is that the solid surface might not be stationary in the terrestrial reference frame. RSLR can be negative because the land is rising, like in areas of Scandinavia near the centre of the former ice sheet. That makes the distinction between this quantity and geocentric sea level rise.

I agree with your preference for "solid surface" over "sea floor". Hence my current preference would be mean_sea_level_rise_wrt_solid_surface (which could be a negative number).

Best wishes

Jonathan

[JonathanGregory]

Dear Stéphane @slawchune

Thanks for your explanation. That clarifies what you mean for me i.e. the IB correction itself, not the corrected SSH. In that case, as you say, a reference level is not needed. We have two existing standard names

sea_surface_height_correction_due_to_air_pressure_and_wind_at_high_frequency sea_surface_height_correction_due_to_air_pressure_at_low_frequency

On the pattern of these, I think the quantity you mean would be named sea_surface_height_correction_due_to_air_pressure. However, others have made the comment, on our sea level terminology paper, that "correction" isn't a good phrase to use. The data is no more "correct" if the "correction" is applied; it's just a different quantity! Hence I will propose renaming these existing standard names.

Would you and others find sea_surface_height_increase_due_to_air_pressure_decrease a clear name for this quantity?

Best wishes

Jonathan

[slawchune]

Hi Jonathan, thank you very much with your help with this !

I would prefer "sea_surface_height_correction_due_to_air_pressure" because it stays general.

"sea_surface_height_increase_due_to_air_pressure_decrease" gives the idea that only low pressure system are considered.

actually we compute the inverted barometer at a 1h frequency. So do you think it would make sense to use "sea_surface_height_correction_due_to_air_pressure_and_wind_at_high_frequency"

Cheers, Stéphane

[taylor13]

On the small point of "change" vs. "rise" for sea level, I think we should be explicit as to the sign, so "rise" would be better.

The remainder of this post is off-topic, due to @JonathanGregory's confusion of two issues (described below).

Similarly, we should find a way to word "sea_surface_height_correction_due_to_air_pressure_and_wind_at_high_frequency" to make it also unambiguous. I agree with Jonathan, that "correction" is vague (and possibly inappropriate), and that we need to specify what is considered "positive" vs. "negative". And "high frequency" depends entirely on context, which leaves it open to misinterpretation.
The frequency should be evident from the time coordinate attached to the variable, so I would leave the "frequency part" off.
Perhaps "adjustment" rather than "correction" might somehow be incorporated?

[JonathanGregory]

Dear @ClemensSchannwell, @slawchune, @taylor13

After replying to @ClemensSchannwell above, I accidentally posted a reply to @slawchune in this issue which should have been in cf-convention/vocabularies#38, and he and @taylor13 replied here. I have hidden these three messages as off-topic, and copied them to cf-convention/vocabularies#38, where they should have appeared. Apologies for the mess.

Best wishes

Jonathan

[JonathanGregory]

Seeing that we have existing standard names

halosteric_change_in_mean_sea_level steric_change_in_mean_sea_level thermosteric_change_in_mean_sea_level

I think change_in_mean_sea_level_wrt_solid_surface would be better. We can clarify in the definition that a positive number means sea-level rise. Is that OK with you, @ClemensSchannwell, @taylor13 et al.?

[ClemensSchannwell]

I would be happy with this definition.

[efisher008]

Hi all,

I have changed the proposed name in the CF editor to change_in_mean_sea_level_wrt_solid_surface.

Best, Ellie

[efisher008]

Hi @ClemensSchannwell,

Are you now happy with the proposed definition for change_in_mean_sea_level_wrt_solid_surface? "The change in local mean sea level relative to the local solid surface, i.e. sea floor. The abbreviation "wrt" means "with respect to". A positive value means sea level rise."

A phrase was added to clarify the acronym 'wrt'. If so, this change can be accepted after a further 7-day period.

Best wishes, Ellie

[ClemensSchannwell]

Hi @efisher008 , Apologies for the late reply. Yes, I am happy with this definition.

Cheers, Clemens

[efisher008]

Dear Clemens,

Some time has now passed and this name has been accepted in the CF editor. It will be published in the next release of the standard names table (v86, anticipated for summer 2024). Thank you again for your proposal!

Best wishes, Ellie

[efisher008]

This has been published in v86 of the Standard Names Table (released 5 September 2024).