Standard names: probability_of_sea_ice_area_fraction_higher_than_0.1 and probability_of_sea_ice_area_fraction_higher_than_0.2

[Aaambroise]

Date 13/11/2025

Hello, I'm Ambroise Albert from the Copernicus Marine service, and I would like to propose the addition of a new alias for this variable Probability of sea ice concentration higher than 10 %.
Here the new standard_name: probability_of_sea_ice_area_fraction_higher_than_0.1

• Variable: Probability of sea ice concentration higher than 10 %
• variable name: siconc10pc
• description: Probability of sea ice concentration higher than 10 % produced using data-driven post processing
• units: 1
  i would also like to propose the addition of a new alias for this Variable: Probability of sea ice concentration higher than 20 %.
  -Here the new - standard_name: probability_of_sea_ice_area_fraction_higher_than_0.2
• variable name: siconc20pc
• description: Probability of sea ice concentration higher than 20 % produced using data-driven post processing
• units: 1
  Thanks for your your help

[github-actions]

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]

Dear @Aaambroise

Thanks for your proposal. Standard names don't contain numerical values, which are instead recorded as coordinates in CF metadata. The existing standard name fraction_of_time_with_sea_ice_area_fraction_above_threshold might be what you need, with a coordinate variable or scalar coordinate variable with the standard name of sea_ice_area_fraction and a value of 0.1 or 0.2. By "probability" do you mean "fraction of time", as I'm assuming?

Best wishes

Jonathan

[JonathanGregory]

In #294 @Aaambroise wrote:

... interpreting these quantities as “fraction of time” would be misleading, since they represent a more generic probability space. For example, a probability of 50% does not imply that the phenomenon occurred halfway through the period considered (as in the classic Schrödinger’s cat analogy). To comply with the rule of avoiding numerical values in standard names, their updated suggestion is: probability_of_sea_ice_area_fraction_above_threshold

This standard name would be used for both variables currently labelled siconc10pc and siconc20pc. Do you confirm that using the same standard name for both variables is acceptable, provided that the threshold is described elsewhere?

Regarding how to encode the threshold (0.1 or 0.2 sea-ice concentration), the producer suggests storing it as a scalar coordinate variable. This seems consistent with CF conventions, but we would appreciate your guidance on the cleanest way to write this in practice.

Yes, I appreciate that "fraction of time" is a restricted sort of probability. probability_of_sea_ice_area_fraction_above_threshold would also be fine, I think. There is one other existing standard name mentioning probability in this sense.

Yes, it is perfectly fine and normal to have more than one variable with a given standard name, if they are distinguished by other metadata. (Even if they aren't, it's allowed, but not so well-described!)

Yes, a scalar coordinate variable is used in other such situations, where a quantity depends on a scalar value, with an appropriate standard name (sea_ice_area_fraction in this case). Usually the description of the standard name states that it expect there to be a coordinate variable of a certain standard name. You could just as well use a size-one (dimensioned) coordinate variable; they mean the same. In addition, since the two quantities have the same standard name and are distinguished by a coordinate value, you could (if you wanted to) put them in one data variable, with a coordinate dimension of 2 for the threshold.

Best wishes, Jonathan

[github-actions]

This issue has had no activity in the last 3 weeks. Accordingly:

• If you proposed this issue or have contributed to the
  discussion, please reply to any outstanding concerns.
• If there has been little or no discussion, please comment
  on this issue, to assist with reaching a decision.
• If the proposal seems to have come to a consensus, please
  wait for the moderators to take the next steps towards
  acceptance.

Standard name moderators are also reminded to review @feggleton @japamment

[Aaambroise]

Hi
Just a quick follow-up on issue #293 to check whether the updated proposal is now considered OK:
Could you please confirm this is the correct CF-compliant approach and that the request has been taken forward?

Many thanks,
Ambroise Albert (Copernicus Marine Service)

[JonathanGregory]

@Aaambroise. What is the updated proposal? Would probability_of_sea_ice_area_fraction_above_threshold be OK for you, with a scalar or size-one coordinate of sea_ice_area_fraction to specify 10%?

[Aaambroise]

Dear @JonathanGregory , probability_of_sea_ice_area_fraction_above_threshold is OK
Dimensions (x,y,time,sea_ice_area_fraction)
With a scalar coordinate of sea_ice_area_fraction to specify either 10% or 20%.
Unit: 1
thank you

[JonathanGregory]

OK, good. Alison @japamment (manager of standard names) will take the proposal forward when she has time, but since no-one has raised concerns I think you can assume it will be agreed. Thanks, @Aaambroise.

[eileenhertwig-dkrz]

Dear @Aaambroise ,

I have added the following term to the CF standard names editor (https://cfeditor.ceda.ac.uk/proposal/5755/):

probability_of_sea_ice_area_fraction_above_threshold:
Sea ice area fraction is area of the sea surface occupied by sea ice. It is also called "sea ice concentration". "probability_of_X" means the chance that X is true or of at least one occurrence of X. Space and time coordinates must be used to indicate the area and time-interval to which a probability applies. "Sea ice" means all ice floating in the sea which has formed from freezing sea water, rather than by other processes such as calving of land ice to form icebergs. "Area fraction" is the fraction of a grid cell's horizontal area that has some characteristic of interest. It is evaluated as the area of interest divided by the grid cell area, or if the cell_methods restricts the evaluation to some portion of that grid cell (e.g. "where sea_ice"), then it is the area of interest divided by the area of the identified portion. It may be expressed as a fraction, a percentage, or any other dimensionless representation of a fraction.
Unit: 1

Does this look okay for you? Do you have any further comments?

Best regards,
Eileen

[JonathanGregory]

Thanks, @eileenhertwig-dkrz. I think the description also needs a statement that there should be a coordinate variable or scalar coordinate variable of sea_ice_area_fraction to specify the threshold.