Standard names: 7 New Flux Variables

[nanderson123]

Updated post (2/24/2023, with final update 6/12/2023)

From the feedback received here and at PMEL, a couple of changes have been made to the descriptions and suggested standard names, which appear in the same order as the original list, which is retained below.

The 3/28/2023 update notes that CF standard names formatted as "difference_between_X_and_Y" indicate X - Y, and this is now clarified in the descriptions of each difference variable below.

Difference_between_sea_surface_subskin_temperature_and_sea_surface_foundation_temperature (°C) ●This variable quantifies the temperature difference between the top and bottom of the diurnal warm layer (computed as sea_surface_subskin_temperature minus sea_surface_foundation_temperature). This difference includes the full contribution of any diurnal warm layer that has developed in the top few meters of the ocean through the absorption of solar radiation, if surface mixing is sufficiently weak.

Difference_between_sea_surface_subskin_temperature_and_sea_surface_temperature (°C) ●This variable quantifies the temperature difference between the top of the diurnal warm layer and the sea surface temperature at depth (computed as sea_surface_subskin_temperature minus sea_surface_temperature). This difference may include a contribution from all or part of any diurnal warm layer that has developed in the top few meters of the ocean through the absorption of solar radiation, if surface mixing is sufficiently weak.

Difference_between_sea_surface_skin_temperature_and_sea_surface_subskin_temperature (°C) ●This variable quantifies the temperature difference between the skin temperature and the subskin temperature (computed as sea_surface_skin_temperature minus sea_surface_subskin_temperature) due to the turbulent and radiative heat fluxes at the air-sea interface. This difference is commonly referred to as the “cool skin effect” as the solar radiation absorbed within the very thin thermal subskin layer is typically negligible compared to ocean surface heat loss from the combined sensible, latent, and net longwave radiation heat fluxes.

atmosphere_obukhov_length (m) ●The height in the atmosphere, L, that buoyant production or destruction of turbulent energy balances the shear production of turbulent kinetic energy: L = -u3 / (kB0), where u is the wind frictional velocity, k is the von Karman constant, and B0 is the atmospheric surface buoyancy flux. If the buoyancy flux is destabilizing, L is negative.

ocean_obukhov_length (m) ●The depth in the ocean, L, that buoyant production or destruction of turbulent energy balances the turbulent kinetic energy: L = -u3 / (kB0), where u is the oceanic surface frictional velocity, k is the von Karman constant, and B0 is the oceanic surface buoyancy flux. If the buoyancy flux is destabilizing, L is negative.

surface_buoyancy_flux_into_air (m2/s3) ●A variable quantifying net density gains or losses in air parcel buoyancy based on turbulent heat and moisture fluxes, represented by virtual temperature flux, at the air-sea interface. Positive values indicate a buoyancy flux out of the ocean (into the air) that will destabilize the atmosphere.

surface_buoyancy_flux_into_sea_water (m2/s3) ●A variable quantifying net density gains or losses in water parcel buoyancy based on thermal (net surface heat flux) and haline (precipitation minus evaporation) forcings at the air-sea interface. A positive value indicates a buoyancy flux into the ocean that will stabilize (i.e., stratify) the surface ocean layer.

Original post (2/1/2023)

A list of 7 new CF standard names is proposed below. The list was compiled by investigating which flux variables contained in OceanSITES data center files did not yet have a CF standard name. The collection largely consists of outputs from the COARE algorithm, and has been vetted by flux experts at (and outside) PMEL, the OASIS FAIR Theme Team, and members of OceanSITES. Proposed terms are listed with their suggested units (in parentheses), followed by a bullet containing their descriptive paragraph. A Word doc is also attached, as some characters fail to render on GitHub. Please contact me with any questions or concerns (Nathan Anderson, nathan.anderson@noaa.gov).

warm_layer_tskin_minus_foundation_SST (°C) ● This variable quantifies the total temperature difference between the top (sea_surface_subskin_temperature) and bottom (sea_surface_foundation_temperature) of the warm layer. This temperature difference between the sea_surface_foundation_temperature and the sea_surface_subskin_temperature is explained by 2 processes: a warm layer and cool skin effect. Warm layers develop as solar radiation warms the upper few meters of ocean more strongly than underlying water during the day, and the resulting temperature profile can become stratified enough to suppress shear-induced mixing, resulting in a diurnal warm layer.

warm_layer_tskin_minus_SST_at_depth (°C) ● Depending on the measurement depth and the presence of a diurnal warm layer, this correction is applied to the in-situ (measured) ocean temperature to obtain the subskin temperature at the air-sea interface (sea_surface_subskin_temperature). Warm layers develop as solar radiation warms the upper few meters of ocean more strongly than underlying water (usually during the day), and the resulting temperature profile can become stratified enough to suppress shear-induced mixing, resulting in a diurnal warm layer.

cool_skin_temperature_correction (°C) ● This variable is the temperature difference between the sea_surface_skin_temperature and the sea_surface_subskin_temperature. Differences between the in-situ (measured) SST at a depth and the ocean surface skin temperature are explained by 2 processes: a warm layer and cool skin effect. The uppermost layer of surface water is frequently cooler than the measured temperature because of the combined cooling effects of sensible heat flux, latent heat flux, and net longwave radiation, which predominantly transfer heat from ocean to atmosphere. To account for this effect, a cool skin correction is applied to measured SST to obtain the temperature at the air-sea interface.

atmospheric_obukhov_stability_height (m) ● The height in the atmosphere, L, that buoyant production or destruction of turbulent energy balances the shear production of turbulent kinetic energy: L = -u3 / (kB0), where u is the wind frictional velocity, k is the von Karman constant, and B0 is the atmospheric surface buoyancy flux. If the buoyancy flux is destabilizing, L is negative.

oceanic_obukhov_stability_depth (m) ● The depth in the ocean, L, that buoyant production or destruction of turbulent energy balances the turbulent kinetic energy: L = -u3 / (kB0), where u is the oceanic surface frictional velocity, k is the von Karman constant, and B0 is the oceanic surface buoyancy flux. If the buoyancy flux is destabilizing, L is negative.

air_surface_buoyancy_flux (m2/s3) ● A variable quantifying net density gains (or losses) in air parcel buoyancy based on thermal (heat flux) and moisture forcings, represented by virtual temperature flux, at the air-sea interface. Positive values indicate a buoyancy flux out of the ocean (into the air) that will destabilize the atmosphere.

sea_surface_buoyancy_flux (m2/s3) ● A variable quantifying net density gains (or losses) in water parcel buoyancy based on thermal (heat flux) and haline (precipitation minus evaporation) forcings at the air-sea interface. A positive value indicates a buoyancy flux into the ocean that will stabilize (stratify) the surface ocean layer.

Nathan Anderson (nanderson123) CF Standard Names for Flux Variables.docx CF standard names (2-24-2023).docx

[JonathanGregory]

Dear Nathan @nanderson123

Thank you for your proposals. I wonder whether the definitions for the second and third are exchanged? Also is the Obukhov stability height/depth the quantity which is called Obukhov length in the AMS glossary?

Best wishes

Jonathan

[nanderson123]

Jonathan @JonathanGregory

The 2nd and 3rd definitions are correct, but perhaps the definitions should be trimmed to keep the warm layer and cool skin terminology separated. It was natural to combine these two related concepts, with the warm layer correction applied first (if a warm layer exists) to correct from the in-situ T to the subskin T, and the cool skin correction applied to get from subskin T to skin T, which is felt by the atmosphere. However, I understand this could confuse users. I will revisit the text with my team at PMEL, and welcome suggestions.

In response to your question: Yes, the stability height/depth is synonymous with the Obukhov length.

Regards, Nathan

[lizkent]

Hi Nathan,

Is warm_layer_tskin defined somewhere?

I see (http://cfconventions.org/Data/cf-standard-names/current/build/cf-standard-name-table.html) that the currently defined skin variables are: sea_surface_skin_temperature & sea_surface_subskin_temperature

Liz

[JonathanGregory]

Dear Nathan @nanderson123

I think the temperature-difference quantities would be more self-explanatory, and more consistent with CF standard names and guidelines, if they used the existing names that you refer to in the definitions:

difference_between_sea_surface_subskin_temperature_and_sea_surface_foundation_temperature
difference_between_sea_surface_subskin_temperature_and_sea_surface_temperature
difference_between_sea_surface_skin_temperature_and_sea_surface_subskin_temperature

Those are quite laborious, but they wouldn't be longer than some other standard names, and there's no doubt what they mean, I would say (given the definitions of the quantities involved).

Is there a reason not to use the usual term "Obukhov length"? We could call these atmosphere_obukhov_length and ocean_obukhov_length.

The buoyancy fluxes are both at the same surface. We already have standard names containing the phrase into_sea_water e.g. for the virtual salt flux. On this pattern, I would suggest surface_buoyancy_flux_into_air and surface_buoyancy_flux_into_sea_water. Would that make sense?

Best wishes

Jonathan

[nanderson123]

Hi Liz, Warm_layer_tskin isn't defined -- we initially wanted a short, concise CF name for the 2x flavors of the warm layer correction. But I'm coming around to the longer naming style (and possibly excluding "warm_layer" from the standard name).

Jonathan, I'm in favor of most of these naming recommendations. One concern, which was brought up in discussions with OASIS, was that "difference" is more ambiguous than "minus". We can ensure the sign convention is clear in the descriptions, but would any of the following be an option?

sea_surface_subskin_temperature_minus_sea_surface_foundation_temperature sea_surface_subskin_temperature_minus_sea_surface_temperature sea_surface_skin_temperature_minus_sea_surface_subskin_temperature

Also, as comments come in here, should I edit my initial post to reflect these name changes? Or re-post the updated bulleted list?

Regards, Nathan

[JonathanGregory]

Dear Nathan @nanderson123

Sometimes people edit the initial post. If you decide to do that, I think it's helpful to retain the original version of it there as well, so that the discussion can be understood later. Reposting the updated list is also helpful. You can do both!

I suggested difference_between_X_and_Y because there are a few existing standard names that include this construction, but we do not mention it in the guidelines, where it should be added. I guess that readers would generally understand it to mean X-Y rather than Y-X but I agree there is an ambiguity. I think it would be OK to say X_minus_Y in these names.

Best wishes

Jonathan

[ngalbraith]

I agree that using the existing standard name sea_surface_foundation_temperature in the new standard names is preferable to abbreviating it to foundation_SST; also that adding a guideline for difference is a great idea. The way difference is calculated could also be in the definitions of these new difference terms.

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[JonathanGregory]

I think this issue is waiting for the proposer Nathan @nanderson123 to summarise the current version. I don't see any disagreements to be addressed, so I expect the proposal could quickly be accepted. On a point previously discussed, I feel that it's better to follow the existing pattern difference_between_X_and_Y, and make clear that this means X-Y both in the definition and in the standard name guidelines.

[lizkent]

Hi,

If the normal convention is difference between rather than minus, and that is clearly defined, then there seems to me to be no need to make this a special case.

One thing I am unclear about is whether a definition of a difference between two already existing variables is automatically defined? In that case there isn't much to do for the temperatures.

On a scientific point I would say that the foundation temperature isn't what is required for fluxes (certainly from a measurement perspective), we need temperature at a known depth (typically what is measured), sea_surface_skin_temperature & sea_surface_subskin_temperature and differences between each of them. If the foundation temperature differences are required from a modelling perspective then they should be added.

Thanks, Liz

[JonathanGregory]

Dear @lizkent

Thanks for your comment. To answer your question: no standard names are defined automatically. Defining a name for the difference between X and Y does not require X and Y to be existing standard names. Even if X and Y have been defined, the name for their difference has to be defined as well, if there's a use case. In general, we don't add standard names to the table that haven't been requested.

Best wishes

Jonathan

[taylor13]

I think it would be o.k. to allow use of either "difference between" or "minus" in standard_names. Whatever is decided, I strongly support the suggestion in https://github.com/cf-convention/vocabularies/issues/156 to make clear what "difference between" means.

For the names already defined with "difference between", there are two different constructions used:

1. "difference between [quantity 1] and [quantity 2]"
2. "[quantity] difference between [two different media or evaluated in 2 different ways]"

For example:

1. difference_between_sea_surface_temperature_and_air_temperature
2. surface_carbon_dioxide_partial_pressure_difference_between_air_and_sea_water

My preference would be to use "minus" in place of the first construction (so, the example becomes sea_surface_temperature_minus_air_temperature and retain "difference between" in the second construction, but I don't think we necessarily have to be prescriptive about this.

[JonathanGregory]

Dear Karl @taylor13

I tend to prefer difference (and have proposed it previously) to minus for these reasons:

• I think it's slightly easier to read "difference between X and Y" because "difference between" signals that the construction is coming up, whereas with "minus" you don't discover that until later.

• It resembles a few other constructions we use, such as "product of X and Y" and "ratio of X to Y".

• It makes a phrase which describes what the quantity is, whereas "minus" describes a recipe for calculating it.

• We haven't so far used "X minus Y", and generally we follow existing patterns if they are suitable.

Best wishes

Jonathan

[taylor13]

My preference for "minus" in the first case above was that it resulted in a shorter, easily interpreted name, but I do not feel strongly about this, so if no one else provides compelling arguments against Jonathan's preference, let's go with it.

[nanderson123]

The proposed standard names were updated on 2/24/2023 based on feedback within this github issue, with added input from our team at PMEL. Ambiguous or previously undefined vocabulary (e.g. warm_layer_tskin) was replaced, and a few terms were simplified (e.g. ocean vs oceanic). Edits appear in the initial post, which was split into sections ('Original Post' and 'Updated Post').

Addressing recent comments, there exist 2 competing convention ideas: X_minus_Y and difference_between_X_and_Y. I initially favored X_minus_Y, but don't have a strong conviction if difference is the accepted format. I will edit the updated post to reflect this, and agree with the suggestion to formally recognize "difference_between_X_and_Y" as always indicating X - Y.

After this edit, the names in the updated post will be ready for acceptance in my view.

-Nathan

[lizkent]

Difference_between_sea_surface_subskin_temperature_and_sea_surface_temperature (°C) ●This variable quantifies the temperature difference between the top of the diurnal warm layer (sea_surface_subskin_temperature) and the in-situ measured sea surface temperature at depth (sea_surface_temperature). A diurnal warm layer can develop in the top few meters of the ocean through the absorption of solar radiation, if surface mixing is sufficiently weak.

I have a couple of comments on this: 1) could the temperature at depth be from a model? Or calculated in some other way? If so suggest dropping the "in situ measured".

2) in the explanation I'm not sure the sentence is clearly enough linked to the variable. Suggest e.g. "This difference may include a contribution from all or part of any diurnal warm layer that has developed in the top few meters of the ocean through the absorption of solar radiation, if surface mixing is sufficiently weak".

Thanks, Liz

[JonathanGregory]

Thanks for the updated proposal, Nathan @nanderson123, and for your subsequent question, @lizkent.

[nanderson123]

All,

I have updated the descriptions to reflect Liz's comments -- thank you for helping us hone these definitions. Because "minus" has been removed from the standard name in favor of "difference between", I made a minor change to each description, making it clear that the difference variables are X-Y.

[JonathanGregory]

Thanks, Nathan @nanderson123. The proposal looks good to me. If there are no further comments soon, I expect that moderators (@feggleton @japamment) will schedule it for inclusion.

[ngalbraith]

Everything looks good to me, though I have a question on the first definition:

"Difference_between_sea_surface_subskin_temperature_and_sea_surface_foundation_temperature (°C)

This variable quantifies the temperature difference between the top and bottom of the diurnal warm layer (computed as sea_surface_subskin_temperature minus sea_surface_foundation_temperature). This diurnal warm layer, caused by absorption of solar radiation in the absence of strong mixing, together with a cool skin effect, account for the total temperature difference between the sea_surface_skin_temperature and the sea_surface_foundation_temperature. The cool skin effect is associated with the turbulent and infrared radiative heat loss at the air-sea interface. Freshwater fluxes may also affect this variable"

Is this too much information that might limit the usefulness of the name? Do we need to include the cause of the difference (solar radiation in the absence of mixing), the definition of cool skin effect ... etc? Why not just

"This variable quantifies the temperature difference between the top and bottom of the diurnal warm layer (computed as sea_surface_subskin_temperature minus sea_surface_foundation_temperature). "?

[ngalbraith]

I still have a minor problem with the detailed description of Difference_between_sea_surface_subskin_temperature_and_sea_surface_foundation_temperature.

Could someone please tell me why we need to provide all this information? It's all interesting, and it's all true - in the way some CF users are currently using the term - but the difference is the difference, and I'm not sure we need to go further that describing X, Y and their relationship (difference).

This clearly needs to be included: This variable quantifies the temperature difference between the top and bottom of the diurnal warm layer (computed as sea_surface_subskin_temperature minus sea_surface_foundation_temperature).

I'm just not sure why this should not be part of the definition: This diurnal warm layer, caused by absorption of solar radiation in the absence of strong mixing, together with a cool skin effect, account for the total temperature difference between the sea_surface_skin_temperature and the sea_surface_foundation_temperature. The cool skin effect is associated with the turbulent and infrared radiative heat loss at the air-sea interface. Freshwater fluxes may also affect this variable.

It's not a deal breaker, I'd just like to know why it's being included. Does it prevent confusion or is it just ... informational? Thank you!

[lizkent]

@ngalbraith Informational I think, the 2 variables in the difference are already defined, the text explains (perhaps) why we want to specifically define the difference itself. I guess its a matter of opinion how useful that is. I felt that information was useful for the difference at depth, this feels a little less useful to me. Following the same lines as the other difference variable perhaps we can say:

"This difference includes the full contribution of any diurnal warm layer that has developed in the top few meters of the ocean through the absorption of solar radiation, if surface mixing is sufficiently weak"

That has the benefit of making the difference between the two definitions clearer.

Liz

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[nanderson123]

Liz, Nan, and all:

I ran this by the PMEL team working on CF names, and they agree with the suggested edit for brevity (previously, it contained several informational sentences, some of which were outside the scope of defining the variable). I've updated the first bulletpoint at the top of this discussion. It now reads:

Difference_between_sea_surface_subskin_temperature_and_sea_surface_foundation_temperature (°C) ●This variable quantifies the temperature difference between the top and bottom of the diurnal warm layer (computed as sea_surface_subskin_temperature minus sea_surface_foundation_temperature). This difference includes the full contribution of any diurnal warm layer that has developed in the top few meters of the ocean through the absorption of solar radiation, if surface mixing is sufficiently weak.

Regards, Nathan Anderson

[lizkent]

Hi, that looks fine to me, thanks Liz

From: nanderson123 @.> Date: Monday, 12 June 2023 at 16:15 To: cf-convention/discuss @.> Cc: Kent, Elizabeth C. @.>, Mention @.> Subject: Re: [cf-convention/discuss] Standard names: 7 New Flux Variables (Issue cf-convention/vocabularies#156)

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Liz, Nan, and all:

I ran this by the PMEL team working on CF names, and they agree with the suggested edit for brevity (previously, it contained several informational sentences, some of which were outside the scope of defining the variable). I've updated the first bulletpoint at the top of this discussion. It now reads:

Difference_between_sea_surface_subskin_temperature_and_sea_surface_foundation_temperature (°C) ●This variable quantifies the temperature difference between the top and bottom of the diurnal warm layer (computed as sea_surface_subskin_temperature minus sea_surface_foundation_temperature). This difference includes the full contribution of any diurnal warm layer that has developed in the top few meters of the ocean through the absorption of solar radiation, if surface mixing is sufficiently weak.

Regards, Nathan Anderson

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[nanderson123]

@JonathanGregory @feggleton @japamment

I believe all comments have been addressed and a consensus reached on this thread. The original post (Feb 24) was updated on June 12 to reflect the finalized variables and descriptions. Please contact me or email Nathan.anderson@noaa.gov if anything further is needed for integration into CF.

Thank you, Nathan Anderson

[JonathanGregory]

Dear Nathan @nanderson123

I agree that this proposal is ready for adoption. I expect the moderators will include it soon in an update to the standard name table. Thank you for your work on it.

Best wishes

Jonathan

[efisher008]

Hi @nanderson123,

I have added the set of original proposed names and definitions to the CF editor, and then updated the names and definitions according to the updated post (2/24/2023) at the top of the page. The latest proposal looks good and follows the CF conventions for constructing standard names; I would just point out that upper case is not used, so all names starting with 'Difference' would simply be changed to 'difference'. Assuming that there are no objections to this change, given that a consensus has been reached in all other areas the names will be approved within the next 7 days. Thank you again for your patience and for thoroughly documenting the changes made during discussion.

Best wishes, Ellie

[efisher008]

Hello @nanderson123,

As there has been no further discussion, these names have been marked as accepted and will be included in the next standard names release. Thanks again.

Best regards, Ellie

[efisher008]

This issue has been closed as the above names were published in version 84 of the standard names table (visible here).