No term for mass fraction of solid water in the atmosphere (not that I found anyway)

[bjorn-stevens]

Bjorn Stevens

2023-07-30

mass_fraction_of_solid_water_in_air

There are related variables, but they propose to link this, or related terms, i.e., ice, to cloud. However solid water (ice) is not necessarily confined to clouds, as anyone hit by a hailstone will attest. Moreover, in models and observations it can be ambiguous to determine what is a cloud. Hence the in air. The use of 'solid_water' is for symmetry with 'liquid_water' and avoids ambiguity with ice, which sometimes has a special meaning (i.e., pristine ice, rather than aggregates, graupel, hail etc). Using frozen water, per the terminology seems like another alternative, but it lacks symmetry with liquid water, and could be called deposition water if it isn't really from freezing. Alas, solid water is complicated.

Units would be 1 (i.e., unitless)

[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]

Dear @bjorn-stevens

Thanks for your proposal. I agree that we don't have a standard name for this quantity, nor for liquid water in air, though we do have one for water (in all phases) in air. You are right that the guidelines suggest frozen_water should be used instead of "ice". Another reason for not using just "ice" is that "ice" might not mean water. It could be carbon dioxide (dry) ice or nitrogen ice, for instance, on other worlds. (CF isn't just used for datasets of Earth science.) Since frozen_water has already been used in a few standard names for soil quantities, it would be consistent and therefore preferable to make it mass_fraction_of_frozen_water_in_air, I think. Would that be acceptable to you?

Best wishes

Jonathan

[bjorn-stevens]

Dear @JonathanGregory

this sounds like a great solution. Thanks for the consideration and suggestion -- Cheers, Bjorn

[JonathanGregory]

I think you're right in suggesting that "frozen water" might be confusing in air, because (as you say) it might have been produced by deposition (vapour to solid) rather than freezing (liquid to solid). I suppose this is less likely to be problematic for ice in soil, which probably percolated as liquid and then froze. If this is a difficulty, perhaps your suggestion of "solid water" is better. I am sure this possibility must have been considered >20 years ago for the guidelines, and I can't remember if there are snags with it. Do you have any other thoughts? Does anyone else have a comment?

[taylor13]

I think even most scientists would interpret "frozen_water" as water being in the solid state without regard to how it got that way, so that would be quite acceptable. "solid_water" would be o.k. too, I think, but superficially at first reading brings to mind a solid block of water rather than a collection of relatively little particles. Another option, I suppose, would be "water_ice" to eliminate the ambiguity Jonathan mentioned above. Or "solid_state_water", which doesn't bring to mind a block of ice. I guess at this point my (weak) preference would be "frozen_water"

[JonathanGregory]

Thanks, Karl. solid_phase_water occurred to me as another possibility along similar lines, but my preference is also for frozen_water, since it's already in use, provided it's not going to cause confusion.

[taylor13]

We can, of course, clarify in the "description" what we mean so there is no chance of misinterpretation. Do you think anyone will ever want to keep track of only the solid-phase water that originated through freezing of liquid? I don't, but If I'm wrong, we should think about what standard name could be given to such a variable. (mass_fraction_of_water_frozen_from_liquid_in_air??) Probably not worth any more of our time though.

[bjorn-stevens]

The problem with water frozen from liquid is that it can be rather ambiguous. Imagine a liquid drop freezing, and then experiencing deposition. Part of the frozen water would be frozen from liquid, part would be from deposition, so then the same mass would have to be fractionated by origin which hardly anyone would want to keep track of if they could. The issue came up for me because we have different species of solid water (ice, snow, graupel, hail) and (cloud, rain, liquid coating of graupel and hail) of liquid water. However for many thermodynamic calculations the internal energy (or enthalpy, depending on coordinates) is needed, and this just depends on the total amount of water in the liquid or solid phases. Water is such an ambiguous quantity as it it refers to both the matter and its phase depending on context, and so I think that we will necessarily have to live with sub-optimal solutions. Wikipedia tends to speak of the liquid and solid phase, but also of the ice, water and steam phases. Ice is ambiguous because there are many solid phases of water, so to be precise one would have to say which one. My brief perusal of usage has solid paired with liquid and gas, and ice paired with water and steam. Both fail as water is actually a vapor (at Earth temperatures). All of which to say is that I would trust your intuition and experience and sense of consistency.

[efisher008]

Hi @bjorn-stevens,

Thank you for your proposal which @feggleton added to the CF editor in September (this is viewable here: https://cfeditor.ceda.ac.uk/proposal/5022/edit). The name has been updated to 'mass_fraction_of_frozen_water_in_air' (current version subject to change). If you have any further suggestions as to a description, please let me know. I hope that we'll be able to come to a satisfactory conclusion about this before too long, as I think it's almost there.

Best regards, Ellie

[efisher008]

Hello @bjorn-stevens,

I have added the following text into the description for your proposed name mass_fraction_of_frozen_water_in_air:

_The phrase "frozen_water" means ice. "Mass fraction" is used in the construction "mass_fraction_of_X_in_Y", where X is a material constituent of Y. It means the ratio of the mass of X to the mass of Y (including X). A chemical species or biological group denoted by X may be described by a single term such as "nitrogen" or a phrase such as "nox_expressed_asnitrogen".

This was from the phrase bank. Please let me know if there is any additional text you'd like to be included in the description.

Best wishes (and a happy new year!), Ellie

[efisher008]

Dear Bjorn @bjorn-stevens,

Are there any further comments on this name or its description you have for us? I think this is close to being agreed.

Thanks and best wishes (and happy summer!), Ellie

[efisher008]

Dear @bjorn-stevens,

I hope you are doing well. There is a related conversation in #22 which might be of interest to you with a similar name atmosphere_mass_content_of_rain/atmosphere_mass_content_of_liquid_precipitation, I think it would be worthwhile to try to keep the related names in both issues as consistent as possible. Please let me know if you have any thoughts on the above description I suggested for the proposed name mass_fraction_of_frozen_water_in_air as it would be useful if this proposal could now reach a conclusion.

Best wishes, Ellie

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