Dear John,

I think the primary defining characteristic is the 3-way partitioning of water 
into liquid, vapor and solid phases. The existing CF standard names referring 
to liquid and vapor phases (e.g. cloud_liquid_water_mixing_ratio, 
rainfall_flux, atmosphere_moles_of_water_vapor, humidity_mixing_ratio) do not 
provide any explanation of the precise definition of these terms -- it is 
assumed that people know what is meant. This is OK if we are not looking at the 
edge cases (e.g. the aggregations of water molecules which occur in vapor at 
high humidity or the details of stratospheric aerosols) -- I'm not an expert 
here either, so I hope we can omit that level of detail here. Existing names 
make reference to snow, hail, graupel, cloud ice and water content of aerosols 
-- I'm not sure it this is 100% complete, but perhaps it is enough to list 
these. Will the following meet your concern:

"Solid precipitation refers to the precipitation of water in the solid phase. 
Water in the atmosphere exists in one of three phases: solid, liquid or vapor. 
The solid phase can exist as snow, hail, graupel, cloud ice, or as a component 
of aerosol."


regards,

Martin


________________________________
From: John Graybeal <jbgrayb...@mindspring.com>
Sent: 13 April 2018 06:32
To: CF Metadata List
Cc: Jonathan Gregory; Juckes, Martin (STFC,RAL,RALSP)
Subject: Re: [CF-metadata] CMIP6 data request: Precipitation of solid phase 
water

I agree with Martin, use solid for atmosphere and frozen for soil. It doesn’t 
jump out at me that solid water is (umm, almost?) always frozen, even though 
it’s obvious that frozen water is always solid.

I think it would be useful if the definition listed the forms (and pathways) 
that solid water can take, so that those of us less atmospherically advanced 
will be able to appreciate what it’s meant to include.

john

---------------------------------------
John Graybeal
jbgrayb...@mindspring.com


> On Apr 6, 2018, at 23:49, Martin Juckes - UKRI STFC 
> <martin.juc...@stfc.ac.uk> wrote:
>
> Dear Jonathan,
>
>
> my vote would be to leave soil water terms unchanged and allow the use of 
> "solid" in the atmosphere.  There is sufficient difference between the 
> behaviour of water in soil and in the atmosphere to justify, in my mind, this 
> slight divergence in usage. After all, solid water from the atmosphere can 
> only become frozen soil water, I believe, by melting, sinking into the soil 
> and then re-freezing,
>
>
> regards,
>
> Martin
>
>
> ________________________________
> From: CF-metadata <cf-metadata-boun...@cgd.ucar.edu> on behalf of Jonathan 
> Gregory <j.m.greg...@reading.ac.uk>
> Sent: 06 April 2018 16:38
> To: cf-metadata@cgd.ucar.edu
> Subject: Re: [CF-metadata] CMIP6 data request: Precipitation of solid phase 
> water
>
> Dear Martin
>
> I agree with you that frozen_precipitation_flux seems a bit more surprising in
> some way than solid_precipitation_flux. If we put "solid" instead of "frozen",
> should we change (by alias) the existing names that have "frozen", which are
>
> frozen_water_content_of_soil_layer
> lwe_thickness_of_frozen_water_content_of_soil_layer
> mass_fraction_of_frozen_water_in_soil_moisture
> mass_fraction_of_unfrozen_water_in_soil_moisture
> soil_frozen_water_content
> surface_frozen_carbon_dioxide_amount
> volume_fraction_of_frozen_water_in_soil
>
> I'm sure there must be others with useful comments to make about this.
>
> Best wishes
>
> Jonathan
>
>
> ----- Forwarded message from Martin Juckes - UKRI STFC 
> <martin.juc...@stfc.ac.uk> -----
>
>> Date: Fri, 6 Apr 2018 15:06:15 +0000
>> From: Martin Juckes - UKRI STFC <martin.juc...@stfc.ac.uk>
>> To: Jonathan Gregory <j.m.greg...@reading.ac.uk>
>> Subject: Re: [CF-metadata] CMIP6 data request: Precipitation of solid phase
>>       water
>>
>> Dear Jonathan,
>>
>>
>> It may be that the situation of interest in soil is a change brought about 
>> by decreasing temperature, and that the nature of the resulting substance is 
>> somewhat complex because of the matrix of soil that is carrying it. In the 
>> atmosphere I feel that applying the term "frozen" is a bit of a stretch, 
>> though I agree that it would be possible to state that as our intended 
>> meaning within the CF convention. On the other hand, we already use "liquid" 
>> (as in cloud_liquid_water) and "vapor" for the other two phases, so there is 
>> an argument for sticking to the standard partition solid/liquid/vapor.
>>
>>
>> Taking your other comments into account, the term would be either 
>> "frozen_precipitation_flux" or "solid_precipitation_flux". 
>> "frozen_precipitation" looks misleading to me, but perhaps that is a matter 
>> of taste.
>>
>>
>> As you say, it would be good to hear other opinions (I'll be on leave for 
>> the next few days, and will pick up the discussion at the end of next week),
>>
>>
>> regards,
>>
>> Martin
>>
>>
>>
>> ________________________________
>> From: CF-metadata <cf-metadata-boun...@cgd.ucar.edu> on behalf of Jonathan 
>> Gregory <j.m.greg...@reading.ac.uk>
>> Sent: 06 April 2018 14:38
>> To: cf-metadata@cgd.ucar.edu
>> Subject: Re: [CF-metadata] CMIP6 data request: Precipitation of solid phase 
>> water
>>
>> Dear Martin
>>
>> That's a good point about snow and ice. I think we should use modified help-
>> text to make clear that "frozen water" means any form of solid water. I can't
>> recall the reason for "frozen" rather than "solid" - I guess because it felt
>> more obvious, if less systematic. I think I'm happy to understand "frozen
>> water" as "water in the solid phase", however it got into that state. I 
>> wonder
>> if others feel differently.
>>
>> Best wishes
>>
>> Jonathan
>>
>> ----- Forwarded message from Martin Juckes - UKRI STFC 
>> <martin.juc...@stfc.ac.uk> -----
>>
>>> Date: Thu, 5 Apr 2018 17:29:08 +0000
>>> From: Martin Juckes - UKRI STFC <martin.juc...@stfc.ac.uk>
>>> To: "cf-metadata@cgd.ucar.edu" <cf-metadata@cgd.ucar.edu>,
>>>       "j.m.greg...@reading.ac.uk" <j.m.greg...@reading.ac.uk>
>>> Subject: Re: [CF-metadata] CMIP6 data request: Precipitation of solid phase
>>>       water
>>>
>>> Dear Jonathan,
>>>
>>>
>>> I hadn't spotted the existing usage of frozen_water. My only reservation is 
>>> that for such names the help text says '"frozen_water" means ice', which 
>>> would exclude snow. The existing usages of "frozen_water" are all soil 
>>> quantities for which the subtlety of the distinction between ice and snow 
>>> is irrelevant. We could modify the help text for atmospheric variables, but 
>>> is the term "frozen" appropriate for all solid phase water in the 
>>> atmosphere?  Freezing is a process of transforming to solid phase through a 
>>> reduction in temperature, which might be considered inappropriate for some 
>>> atmospheric ice and snow formation pathways ... I'm not sure about this, 
>>> what do you think?
>>>
>>>
>>> regards,
>>>
>>> Martin
>>>
>>>
>>> ________________________________
>>> From: CF-metadata <cf-metadata-boun...@cgd.ucar.edu> on behalf of Jonathan 
>>> Gregory <j.m.greg...@reading.ac.uk>
>>> Sent: 05 April 2018 18:18
>>> To: cf-metadata@cgd.ucar.edu
>>> Subject: [CF-metadata] CMIP6 data request: Precipitation of solid phase 
>>> water
>>>
>>> Dear Martin
>>>
>>> I agree with the need, but I note that the guidelines propose the phrase
>>> frozen_water for solid water, and this is already used in several standard
>>> names.
>>>
>>> Although "precipitation" is used in the world at large for species other 
>>> than
>>> water, so far in CF standard names it's used only for water. Hence we can 
>>> omit
>>> "water" for consistency.
>>>
>>> In view of these two points, would frozen_precipitation_flux be OK?
>>>
>>> Best wishes
>>>
>>> Jonathan
>>>
>>> ----- Forwarded message from Martin Juckes - UKRI STFC 
>>> <martin.juc...@stfc.ac.uk> -----
>>>
>>>> Date: Tue, 3 Apr 2018 11:46:50 +0000
>>>> From: Martin Juckes - UKRI STFC <martin.juc...@stfc.ac.uk>
>>>> To: "cf-metadata@cgd.ucar.edu" <cf-metadata@cgd.ucar.edu>
>>>> Subject: [CF-metadata] CMIP6 data request: Precipitation of solid phase 
>>>> water
>>>>
>>>> Dear All,
>>>>
>>>>
>>>> The CMIP6 data request includes a request for a variable representing the 
>>>> precipitation flux of water in a solid phase (including snow and ice). 
>>>> This variable was also in CMIP5. The current CMIP6 data request follows 
>>>> CMIP5 usage in adopting the standard name "snowfall_flux" for this 
>>>> variable, which is not really correct. There may have been a time when all 
>>>> solid precipitation in CMIP models was snow, but I think we need a more 
>>>> precise name now.
>>>>
>>>>
>>>> We have "rainfall_flux" for precipitation of liquid phase water, but in 
>>>> other terms the construction "liquid_water" is used to refer to the liquid 
>>>> phase, e.g. "mass_concentration_of_liquid_water_in_air", so "solid_water" 
>>>> is a natural extension.
>>>>
>>>>
>>>> I propose a new standard name for solid phase precipitation:
>>>>
>>>>
>>>> precipitation_flux_of_solid_water [kg m-2 s-1]
>>>>
>>>> In accordance with common usage in geophysical disciplines, "flux" implies 
>>>> per unit area, called "flux density" in physics. "solid_water" refers to 
>>>> all forms of the solid phase of water.
>>>>
>>>>
>>>> regards,
>>>>
>>>> Martin
>>>> _______________________________________________
>>>> CF-metadata mailing list
>>>> CF-metadata@cgd.ucar.edu
>>>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>>>
>>> ----- End forwarded message -----
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>>
>> ----- End forwarded message -----
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>
> ----- End forwarded message -----
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