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[CF-metadata] New standard names for ESA GHG CCI quantities

From: alison.pamment at stfc.ac.uk <alison.pamment>
Date: Wed, 20 Jan 2016 14:16:56 +0000

Dear Max,

Thank you for your comments. (This reply is also being posted to the CF mailing list so that all subscribers can follow the discussion and contribute).

In CF, different standard names often do sound quite similar as a direct result of our efforts to standardize the use of individual terms and phrases. However, all the terms are carefully defined and full explanations accompany (almost) every entry in the standard name table. We have many existing "atmosphere" and "in_air" names and the distinction between these is precisely that "atmosphere" applies to the whole column, or in some cases the entire atmosphere, whereas "in_air" applies to a local value within the medium. We make a similar distinction in oceanographic names by using "ocean" for column names and "in_sea_water" for local values. Hence, I think it is appropriate to use "atmosphere" for your proposed names. I agree with Jonathan's advice to also attach a cell_methods attribute to your data variable, e.g., cell_methods = "height: mean" or cell_methods = "pressure: mean" depending on your choice of vertical coordinate. This would avoid any confusion about how the quantity was calculated.

Clearly you do have a requirement to distinguish between ambient and dry air, so certainly the name should reflect this. Hence I still favour my suggestions of: dry_atmosphere_mole_fraction_of_methane and dry_atmosphere_mole_fraction_of_carbon_dioxide. The addition of "dry" at the beginning of each name would, as you pointed out, help to further distinguish from the existing "in_air" names. Would this be an acceptable compromise?

Best wishes,
Alison

From: Dr. Maximilian Reuter [mailto:reuterm at loz.de]
Sent: 20 January 2016 13:25
To: Pamment, Alison (STFC,RAL,RALSP); j.m.gregory at reading.ac.uk
Cc: Michael.Buchwitz at iup.physik.uni-bremen.de; Veronika.Eyring at dlr.de; Bennett, Victoria (STFC,RAL,RALSP)
Subject: Re: [CF-metadata] New standard names for ESA GHG CCI quantities

Hi Alison et al.,

thanks for coming back to the XCO2 and XCH4 CF standard names. As mentioned in an earlier mail (18.11.2015), I think atmosphere_mole_fraction_of_carbon_dioxide_in_dry_air could be mixed up with the already existing name "mole_fraction_of_carbon_dioxide_in_air". In contrast to mole_fraction_of_carbon_dioxide_in_air, XCO2 is a column average. At least for me, "atmosphere" would not automatically imply that a column average is meant.

Additionally, it makes a difference if the mole fraction is relative to dry or wet air. The difference is small but in terms of required accuracy for XCO2 and XCH4, the difference is important and was subject to many discussions in the past (see also TCCON<https://tccon-wiki.caltech.edu/Network_Policy/Data_Use_Policy/Auxiliary_Data>). Therefore, I thinks it is important to specify in the standard name that XCO2 (and XCH4) are column averages and that they are dry_air mole fractions.

What about "column_average_mole_fraction_of_carbon_dioxide_in_dry_air"? On the one hand, this would be consistent with the naming convention of "mole_fraction_of_carbon_dioxide_in_air" and on the other hand it would clearly specify the difference to "mole_fraction_of_carbon_dioxide_in_air.

Anyway, I'm happy with any name we can get :)

Cheers Max
____________________________________________________________________
Dr. Maximilian Reuter

Institute of Environmental Physics (IUP)
University of Bremen, FB1
Otto-Hahn-Allee 1
D-28334 Bremen
Germany

Phone: +49 (421) 218 62085
FAX: +49 (421) 218 62070
E-Mail: maximilian.reuter at iup.physik.uni-bremen.de<mailto:maximilian.reuter at iup.physik.uni-bremen.de>
http://www.iup.uni-bremen.de/~mreuter
____________________________________________________________________

Am 20.01.2016 um 13:22 schrieb alison.pamment at stfc.ac.uk<mailto:alison.pamment at stfc.ac.uk>:

Dear Jonathan,



I agree that we don't usually combine "atmosphere" and "in_air" in the same name. My reason for doing it in this case was because the original proposal specified two conditions:

1) dry air;

2) column average quantity (therefore not local).

I needed to find some way of including both in the name. However, it may be that we don't need the "dry" bit at all, in which case we could just go with atmosphere_mole_fraction_of_methane and atmosphere_mole_fraction_of_carbon_dioxide, and there is no problem. If it really is important that we specify "dry" for these quantities, perhaps a better solution would be to put it at the start of the name, thus, dry_atmosphere_mole_fraction_of_methane and dry_atmosphere_mole_fraction_of_carbon_dioxide. Does that look better?



Best wishes,

Alison



-----Original Message-----

From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf

Of Jonathan Gregory

Sent: 19 January 2016 16:55

To: cf-metadata at cgd.ucar.edu<mailto:cf-metadata at cgd.ucar.edu>

Subject: [CF-metadata] New standard names for ESA GHG CCI quantities



Dear Alison



In existing names we generally use "atmosphere" to indicate a property of

the

atmosphere as a whole (or a large portion of it) and "in_air" to indicate a

local property within the atmosphere. We don't use both phrases at once.

These

quantities can be regarded as means of local properties, I think, so just

in_air would be sufficient. If no vertical coordinate is specified, it should

apply to the entire atmosphere, but to make that clear a cell_method could

be

added to record that it's a vertical mean.



Best wishes



Jonathan



----- Forwarded message from alison.pamment at stfc.ac.uk<mailto:alison.pamment at stfc.ac.uk> -----



Date: Tue, 19 Jan 2016 16:39:38 +0000

From: alison.pamment at stfc.ac.uk<mailto:alison.pamment at stfc.ac.uk>

To: cf-metadata at cgd.ucar.edu<mailto:cf-metadata at cgd.ucar.edu>

CC: Veronika.Eyring at dlr.de<mailto:Veronika.Eyring at dlr.de>, victoria.bennett at stfc.ac.uk<mailto:victoria.bennett at stfc.ac.uk>,

    mreuter at iup.physik.uni-bremen.de<mailto:mreuter at iup.physik.uni-bremen.de>,

    Michael.Buchwitz at iup.physik.uni-bremen.de<mailto:Michael.Buchwitz at iup.physik.uni-bremen.de>

Subject: [CF-metadata] New standard names for ESA GHG CCI quantities



Dear All,



I have been asked to re-propose two standard names that were originally

proposed by Maximilian Reuter in 2014 but which did not receive any

comments at the time: http://mailman.cgd.ucar.edu/pipermail/cf-

metadata/2014/057373.html.

I have rephrased the original proposal to make the names more CF like

and have added some standard definition text, so the names are now

proposed as follows:

atmosphere_mole_fraction_of_methane_in_dry_air (canonical units: 1)

'Mole fraction is used in the construction "mole_fraction_of_X_in_Y",

where X is a material constituent of Y. A chemical species denoted by X may

be described by a single term such as "nitrogen" or a phrase such as

"nox_expressed_as_nitrogen". The "atmosphere mole fraction" of a

quantity refers to the column average from the surface to the top of the

atmosphere. Methane is a member of the group of hydrocarbons known as

alkanes. There are standard names for the alkane group as well as for some

of the individual species. The chemical formula for methane is CH4.'

atmosphere_mole_fraction_of_carbon_dioxide_in_dry_air (canonical

units: 1)

'Mole fraction is used in the construction "mole_fraction_of_X_in_Y",

where X is a material constituent of Y. A chemical species denoted by X may

be described by a single term such as "nitrogen" or a phrase such as

"nox_expressed_as_nitrogen". The "atmosphere mole fraction" of a

quantity refers to the column average from the surface to the top of the

atmosphere. The chemical formula for carbon dioxide is CO2.'

These names reflect the original proposal, and generally follow the syntax

of existing names such as mole_fraction_of_carbon_dioxide_in_air. I have

prepended these names with the word "atmosphere" as a way of indicating

a column amount, similar to existing atmosphere_mass_content names.

We don't currently have any "dry_air" names in CF. When this topic last

came up on the mailing list (as far back as 2008 under the thread entitled

"mixing ratio") it was concluded that the current "in_air" names don't tie the

definition down to either dry or ambient air. The reason for this (deliberate)

vagueness is that numerically the quantities in dry or moist air are not very

different except in the case of water vapour itself where we define

humidity_mixing_ratio to mean " ratio of the mass of water vapor to the

mass of dry air". The gist of the 2008 conversation was that if we ever

needed to be very precise about making the distinction between ambient

air and dry air then we would be able to introduce appropriate names at a

later stage, but there wasn't a pressing need at the time. An offline

conversation I had more recently with Jonathan Gregory and Martin Schultz

went along similar lines, basically saying that we wouldn't change any

existing names where the deliberate impre

 ci

 sion isn't important, but reiterating that we could introduce new names if

there are cases where it does matter, specifying dry or ambient.

Please could Maximilan, Veronica or another member of the CCI team

answer the question about whether there is a real need to specify "dry_air"

in the case of these names, or can we get away with being a bit more vague?

If vagueness is OK, then the names would simplify to

atmosphere_mole_fraction_of_methane_in_dry_air and

atmosphere_mole_fraction_of_carbon_dioxide. Also, do others agree with

my using "atmosphere" here to indicate the column average? All comments

are welcome.

Best wishes,

Alison

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