CF standard name for light irradiance

[gdapueto]

Question

I am looking for the correct standard name to associate with the P01 parameter "PCTIRRXX - Proportion of sub-surface irradiance (PAR wavelengths) {Percent light depth}" (https://vocab.nerc.ac.uk/collection/P01/current/PCTIRRXX/)
Could you kindly support me with this?

[sadielbartholomew]

I am not familiar with the domain relating to the parameter in question, but very familiar with the standard names table - so can provide my interpretation in case it helps for now.

On searching for related terms in the current table the most relevant names I find (mostly via '(ir)radiance' as the search term but trying various keywords) are:

• 'downwelling_spherical_irradiance_in_sea_water',
• perhaps 'downwelling_photon_spherical_irradiance_in_sea_water' given it is light irradiance,
• or perhaps most closely corresponding of all, 'downwelling_photosynthetic_photon_spherical_irradiance_in_sea_water' (since photosynthesis is what PAR irradiance relates to if a search on the term guides me correctly?)
• 'surface_downwelling_photosynthetic_photon_spherical_irradiance_in_sea_water' if surface and sub-surface are catered for as per the parameter requirements (but the use of 'surface' in these names is a bit unclear to me).

But the problem is that parameter is dimensionless, being a percent, and none of the terms related to downwelling irradiance cover ratios between them (judging by searching on 'irradiance' and similar terms across the table and checking the units column for anything with '1' there). It may be that a division between two of the above or similar names suffice, but CF standard names are intended to identify the physical quantity rather than simply encode its mathematical construction.

So I suspect a new name would be needed to cater for this parameter, given in short lack of related existing names with the right units, and this could count as a proposal for this.

[gdapueto]

Hi, Thank you for the quick replay and for your explanation. However, I don't think any of the existing standard name are really appropriate for our case. For now we work without a standard name association. Thanks for trying anyway. Best Giulia Giulia Dapueto t. +39 335 8459239 ***@***.*** [cid:8bbc730c-5f82-456b-ae4f-9ce5ac8f5edb] ETT S.p.A. Soc. Contr. Art. 2497 C.C. da Dedagroup S.p.A.(TN) | Via Albareto 21, 16153 Genova - Italy | P.IVA/CF/Reg Impr. Genova 03873640100 t. 010 6519116 | www.ettsolutions.com<https://www.ettsolutions.com/> Non stampare questa e-mail. Questo documento è formato esclusivamente per il destinatario. Tutte le informazioni ivi contenute, compresi eventuali allegati, sono da ritenere esclusivamente confidenziali e riservate secondo i termini del vigente D.Lgs. 196/2003 in materia di privacy e del Regolamento europeo 679/2016 – GDPR- e quindi ne è proibita l’utilizzazione ulteriore non autorizzata. Se avete ricevuto per errore questo messaggio, Vi preghiamo cortesemente di contattare immediatamente il mittente e cancellare la e-mail. Grazie. Please don’t print this e-mail. Confidentiality Notice – This e-mail message including any attachments is for the sole use of the intended recipient and may contain confidential and privileged information pursuant to Legislative Decree 196/2003 and the European General Data Protection Regulation 679/2016 – GDPR-. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies of the original message.

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________________________________ Da: Sadie L. Bartholomew ***@***.***> Inviato: lunedì 24 agosto 2026 16:06 A: cf-convention/discuss ***@***.***> Cc: Giulia Dapueto ***@***.***>; Author ***@***.***> Oggetto: Re: [cf-convention/discuss] CF standard name for light irradiance (Discussion #480) I am not familiar with the domain relating to the parameter in question, but very familiar with the standard names table - so can provide my interpretation in case it helps for now. On searching for related terms in the current table the most relevant names I find (mostly via '(ir)radiance' as the search term but trying various keywords) are: * 'downwelling_spherical_irradiance_in_sea_water', * perhaps 'downwelling_photon_spherical_irradiance_in_sea_water' given it is light irradiance, * or perhaps most closely corresponding of all, 'downwelling_photosynthetic_photon_spherical_irradiance_in_sea_water' (since photosynthesis is what PAR irradiance relates to if a search on the term guides me correctly?) * 'surface_downwelling_photosynthetic_photon_spherical_irradiance_in_sea_water' if surface and sub-surface are catered for as per the parameter requirements (but the use of 'surface' in these names is a bit unclear to me). But the problem is that parameter is dimensionless, being a percent, and none of the terms related to downwelling irradiance cover ratios between them (judging by searching on 'irradiance' and similar terms across the table and checking the units column for anything with '1' there). It may be that a division between two of the above or similar names suffice, but CF standard names are intended to identify the physical quantity rather than simply encode its mathematical construction. So I suspect a new name would be needed to cater for this parameter, given in short lack of related existing names with the right units, and this could count as a proposal for this. — Reply to this email directly, view it on GitHub<#480?email_source=notifications&email_token=BGFA3DLSMVAVKDGY7RHS3ET5LRDWPA5CNFSNUABIM5UWIORPF5TWS5BNNB2WEL2ENFZWG5LTONUW63SDN5WW2ZLOOQXTCOBRGM2TSNBVUZZGKYLTN5XKMYLVORUG64VFMV3GK3TUVRTG633UMVZF6Y3MNFRWW#discussioncomment-18135945>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/BGFA3DIYLW66VW655MVJIM35LRDWPAVCNFSNUABIKJSXA33TNF2G64TZHMYTSMJUGAYDQMJVHNCGS43DOVZXG2LPNY5TCMBWG43TENBVUF3AE>. Triage notifications, keep track of coding agent tasks and review pull requests on the go with GitHub Mobile for iOS<https://github.com/notifications/mobile/ios/BGFA3DIPMV2CLSHWEISTVF35LRDWPA5CNFSNUABIM5UWIORPF5TWS5BNNB2WEL2ENFZWG5LTONUW63SDN5WW2ZLOOQXTCOBRGM2TSNBVUZZGKYLTN5XKMYLVORUG64VFMV3GK3TUVJTG633UMVZF62LPOM> and Android<https://github.com/notifications/mobile/android/BGFA3DK2NK2Z2FCUVBKCURT5LRDWPA5CNFSNUABIM5UWIORPF5TWS5BNNB2WEL2ENFZWG5LTONUW63SDN5WW2ZLOOQXTCOBRGM2TSNBVUZZGKYLTN5XKMYLVORUG64VFMV3GK3TUVZTG633UMVZF6YLOMRZG62LE>. Download it today! You are receiving this because you authored the thread.Message ID: ***@***.***>

[sadielbartholomew]

However, I don't think any of the existing standard name are really appropriate for our case.

It's OK, in this case you are encouraged to request a new name. I will transfer this issue over to the vocabularies repo where it can stand as a proposal. Maybe others might appreciate a new name or name(s) along this line and they can comment too if so.

[sadielbartholomew]

erget or ethanrd I see I am not an 'owner' member of the 'cf-convention' org on GitHub, so don't have the right priveleges, but you two are - would one of you mind transferring this discussion over to the vocabularies repo? You can use the option on the right nav bar at the bottom.

Ignore me sorry, see Jonathan's note below.

[JonathanGregory]

Dear Sadie and Giulia

If a proposal for a new standard name arises from a GitHub Discussion, such as this one, the usual way is to open a new issue in the vocabularies repo and leave the Discussion where it is (not transfer it). The issue can refer back to the Discussion if it's relevant, of course.

Best wishes

Jonathan

[JonathanGregory]

Dear Giulia @gdapueto

I agree with you and Sadie that the existing standard names aren't suitable because none of them are ratios. A new standard name could be proposed. Since this quantity is in the NVS, it's likely others would need it as well. Given the definition, it could accurately be called ratio_of_downwelling_photosynthetic_radiative_flux_in_sea_water_to_surface_downwelling_photosynthetic_radiative_flux_in_sea_water, which conforms to existing patterns, but the repetition makes it very long. I'm sure we can think of a way to shorten it without losing clarity, if you want to proceed with proposing a new standard name.

Best wishes

Jonathan

[sadielbartholomew]

Thanks for clarifying Jonathan.

This thread did remind me of a question I had about standard names, namely whether we standardise in practice the term for a fraction of two quantities of same units/dimensions. I think we should certainly do this, and indeed in your original guidelines for name construction you do specify under 'Transformations' that ratio_of is the way as per your suggestion here. But it looks like most but not all such names get the descriptor ratio_of - notably there are two which use the term 'proportion': 'acoustic_proportion_occupied_in_sea_water' and 'proportion_of_acceptable_signal_returns_from_acoustic_instrument_in_sea_water'. Can we get those and any other dimensionless fractional values updated to ratio_of in line with the rules?

[JonathanGregory]

Dear @sadielbartholomew

Thanks for raising this point. In some cases, I think it is clearer to say that it's a proportion, in order to avoid repetition. For example, the existing standard name fraction_of_surface_downwelling_photosynthetic_radiative_flux_absorbed_by_vegetation could be expressed as ratio_of_surface_downwelling_photosynthetic_radiative_flux_absorbed_by_vegetation_to_surface_downwelling_photosynthetic_radiative_flux, but that would be less easy to comprehend, I feel.

The quantity which @gdapueto has asked about is actually a similar case to that one. We could call it fraction_of_surface_downwelling_photosynthetic_radiative_flux_in_sea_water. I think that would be correct, but maybe not sufficiently informative, because it doesn't indicate what has changed, which makes the numerator of the ratio (the fraction) different from the denominator. fraction_below_surface_of_surface_downwelling_photosynthetic_radiative_flux_in_sea_water seems better to me. We could suggest a guideline of the form: Afraction_of_B or fraction_A_of_B, where B is another standard name, means [the part of B which is specified by A] divided by [the whole of B]. If A is just an adjective, it can go in front of B (except that we must avoid phrases such as mole_fraction and mass_fraction, which have their own special meaning and constructions).

Following that guideline, fraction_of_surface_downwelling_photosynthetic_radiative_flux_absorbed_by_vegetation should be fraction_absorbed_by_vegetation_of_surface_downwelling_photosynthetic_radiative_flux. That's slightly less natural English, but actually I think it's clearer. As it stands, surface_downwelling_photosynthetic_radiative_flux_absorbed_by_vegetation might be understood to be the denominator, leaving it unstated what the numerator is. "Absorbed by vegetation" is A, which characterises the part of B (= "surface downwelling photosynthetic radiative flux") which has been divided by B. To be clear about this, in English, you might well say "fraction of the surface downwelling photosynthetic radiative flux which is absorbed by vegetation", or "fraction which is absorbed by vegetation of the surface downwelling photosynthetic radiative flux". If the guidelines and the description of the individual standard names are clear about the interpretation, we can manage without the extra words which would be needed to make it clearer natural language.

As you say, there are two standard names with proportion. I think we should consider changing them to fraction, which is a word used in many standard names. Following the above suggested guidelines, proportion_of_acceptable_signal_returns_from_acoustic_instrument_in_sea_water would be better expressed as acceptable_fraction_of_signal_returns_from_acoustic_instrument_in_sea_water, where A = acceptable. This means [acceptable signal returns from acoustic instrument in sea water] divided by [signal returns from acoustic instrument in sea water]. Regarding the other one, reading its definition, I don't understand what acoustic_proportion_occupied_in_sea_water means. I feel that this one needs some attention. Thanks for pointing it out.

What do you think, or others @marian-osei92 @eileenhertwig-dkrz?

[sadielbartholomew]

Thanks for clarifying Jonathan. Maybe we can start another issue to discuss those two with proportion and perhaps also formalise what you've said above regarding a ratio_of an fraction_of quantities and how to form standard names with them? Since it's related to, but different from, the issue at hand of this thread.

[JonathanGregory]

@sadielbartholomew, yes, I agree about tackling these in different issues. This conversation is a GtHub Discussion, in which I think some digressions are fine. :-)

Giulia @gdapueto, If you would like to propose a standard name for this quantity, you are welcome to open an issue for it in the vocabularies repo. My suggestion would be fraction_below_surface_of_surface_downwelling_photosynthetic_radiative_flux_in_sea_water but you or others may have better suggestions for words.

Happy weekend. Jonathan

[marian-osei92]

Hello everyone. I have done a bit of digging into this variable and, as this is outside our area of expertise, I wanted to clarify (@gdapueto) whether this parameter is akin to transmission ratio for PAR in sea water as PAR(z)/PAR(0). This quantity is dimensionless and represents the proportion of photosynthetically active radiation (PAR) transmitted from the sea surface to the subsurface water column.

If this interpretation is correct, it may be worth revisiting the variable name. At present, we do not have any variables describing light transmission, and this could provide a useful starting point. @JonathanGregory, the proposed name looks good to me. However, it would be useful to see what @gdapueto suggest as well, particularly to ensure consistency with any established terminology. A small modification: transmission_ratio_subsurface_of_surface_downwelling_photosynthetic_radiative_flux_in_sea_water.

We can explicitly define the transmission ratio term, which could then be reused in future naming conventions, along the line of:
"Transmission ratio (or transmittance) is the ratio of transmitted radiant energy to incident radiant energy. It is a dimensionless quantity and represents the fraction of radiation that passes through a medium."

The variable could then be defined as: "Ratio of downwelling photosynthetically active radiative flux (PAR) at a specified subsurface depth to that at the sea surface, representing the fraction of surface PAR transmitted into the water column."

@JonathanGregory I agree to move this over to the vocab repo if @gdapueto is interested in proposing a name.

PS: The harmonisation of fraction, ratio, and proportion can be revisited, but I would point out that some existing standard names are better with the current terminology. It may therefore be worth discussing this further with the other members (@japamment @feggleton @eileenhertwig-dkrz or at an upcoming conference.

Cheers,
Marian

[JonathanGregory]

Thanks for your investigations, @marian-osei92, and for your suggestion of subsurface. That's better than below_surface, especially because it's an adjective, so we could put subsurface_(transmission_ratio|fraction)_of_surface_downwelling_photosynthetic_radiative_flux_in_sea_water. I agree also that we shouldn't change standard names if they're already clear enough. My concern with the two proportion names is more that I don't think the meaning is clear, not so much about the word proportion. Jonathan