Standard names: *Sea Ice Ridge Ratio*

[abiardeau]

Hello, I am Aurore Biardeau working for Copernicus Marine Service on behalf of Mercator Ocean.

15/06/2023

I would like to submit this standard name for the sea ice volume of ridged ice :

• standard_name : sea_ice_volume_fraction_of_ridged_ice
• long_name : Sea Ice Volume Fraction of Ridged Ice
• units : 1

[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.

[taylor13]

It's not clear to me is this the volume of ridged sea ice divided by the total volume of sea ice?

I would note that there is related discussion, but for the case of area fractions for various "area types" in issue 161. It is noted that since there are dozens of area types defined here, the number of variants of area_fraction could balloon to dozens. To avoid this, an option under CF is to include a scalar dimension containing a string set to the area type of interest (as it appears in the above cited table).

For consistency with this approach, I suggest for your use case, define a new standard name volume_fraction. Then if you want the volume fraction of sea ice that is ridged, you would

1. assign volume_fraction to standard_name
2. include a scalar dimension named, say, "areatype" with its value set to sea_ice_ridges.
3. include in cell_methods: "area: mean where sea_ice".

This approach has the virtue that it can represent area fraction of any of the area types in the CF table of area types. When various volume fractions (e.g., both sea_ice_ridges, and sea_ice_melt_pond) are stored in a single variable, then you simply expand the areatype dimension from size 1 to size 2, and record the two different area types.

[github-actions]

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[efisher008]

Hello @abiardeau,

Would you like to reply to @taylor13's suggestion? If there's any more assistance you require or anything we can help with, please let me know.

Best regards,
Ellie

[abiardeau]

Dear all,

Sorry for the late reply.
Yes this ratio is the volume of ridged sea ice divided by the total volume of sea ice. For example, a value of 0.4 means that 40% of the total volume of sea ice is ridged. So far, we used the variable below but as we try to comply with CF as much as possible, I am happy to read your suggestion.

• standard_name: sea_ice_volume_fraction_of_ridged_ice
• long_name: Sea ice Volume Fraction of Ridged Ice 
• units: 1
• cell_methods: time: mean (interval: 1 hours) area: mean where ice

Best regards,
Aurore

[taylor13]

I was suggesting simply "volume_fractIon" but that would be ambiguous (i.e., fraction of what volume? volume of grid cell? Or volume of sea ice?). I think "sea_ice_volume_fraction" is therefore much better. On the other hand, I think we should consider omitting "of_ridged_ice" and instead include "sea_ice_ridges" as the value of a (in your case scalar coordinate), so you would have, something along the lines of

float seaicevolfrac(time,lat,lon,lbl)
    seaicevolfrac:standard_name="sea_ice_volume_fraction"
    seaicevolfrac:coordinates=seaicetype(lbl)

  string seaicetype(lbl) ;
    seaicetype:long_name="type of seaice"
data:
  seaicetype = "sea_ice_ridges" 

The above approach would work for a variety of different sea ice types without having to define a new standard name each time we wanted to save the volume fraction of a different sea ice type. Of course if you anticipate there will never be more than a few different sea ice types, then maybe its better to define unique standard names for each. But then you wouldn't be able to store all the different sea_ice_volume_fraction(s) in a single variable, as you could with the above approach.

perhaps @JonathanGregory might have time to look at this and provide his perspective.

[JonathanGregory]

Dear Aurore @abiardeau and Karl @taylor13

I understand Karl's concern in principle about large numbers of possible kinds of fraction, but in practice I can't think of many that might arise. I suppose you might want to know the volume fraction of sea ice that was first-year or multi-year, for example. With the area fractions, we started with individual standard names, and later provided the area_types as a generalisation. I suggest that we proceed similarly here, consistent with our principle of not providing new mechanisms until we are certain we need them.

There are some existing standard names for volume types e.g. volume_fraction_of_clay_in_soil, volume_fraction_of_oxygen_in_sea_water. We could follow that pattern, for instance volume_fraction_of_ridged_ice_in_sea_ice. Would that make sense?

Best wishes

Jonathan

[taylor13]

I thought there might be only a few "types", so I'm o.k. with a specific standard name for ridges. And the consistency Jonathan pointed out would argue for his suggested alternative name. Maybe @abiardeau can tell us if that would be acceptable. (It does seem a little odd that the fraction, although expressed as a volume, seems to be determined by a 2-dimensional distribution. That is, if sea ice is ridged, then count the whole depth of sea ice under those ridges, not just the ridged portion on top. Or perhaps the ridges are evident through the thickness of the sea ice? I'm curious.)