Dear Max,
Thank you for your explanation of how the quantity is calculated. Now I understand it better, I think the best approach is *not* to include the cell_methods attribute, which describes statistical processing along a particular axis of your data variable, and instead use the standard name definition to explain how the quantity is obtained. Your explanation describes what I would intuitively expect a column mole fraction to mean, so combining this with the definitions of other CF ?standard phrases? I suggest the following:
dry_atmosphere_mole_fraction_of_methane (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 construction "dry_atmosphere_mole_fraction" means that the quantity refers to the whole atmospheric column and is calculated as the total number of particles of X in the column divided by the number of dry air particles in the same column, i.e. the effect of water vapor is excluded. For localized values within the atmospheric medium, standard names including "in_air" are used. 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.?
dry_atmosphere_mole_fraction_of_carbon_dioxide (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 construction "dry_atmosphere_mole_fraction" means that the quantity refers to the whole atmospheric column and is calculated as the total number of particles of X in the column divided by the number of dry air particles in the same column, i.e. the effect of water vapor is excluded. For localized values within the atmospheric medium, standard names including "in_air" are used. The chemical formula for carbon dioxide is CO2.?
Are these OK?
Best wishes,
Alison
From: Dr. Maximilian Reuter [mailto:reuterm at loz.de]
Sent: 20 January 2016 15:04
To: Pamment, Alison (STFC,RAL,RALSP); j.m.gregory at reading.ac.uk; cf-metadata at cgd.ucar.edu
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,
"atmosphere": I wasn't aware that "atmosphere" usually refers to the whole column in the "CF-world".
cell_method: I don't know what kind of cell methods are allowed. "pressure: mean" comes close but is not exactly the calculated quantity because pressure is only approximately proportional to the number of dry particles. XCO2 is the sum over all CO2 particles in the atmospheric column divided by the number of dry air particles in the same column.
"dry_atmosphere_mole_fraction_of_carbon_dioxide/methane": Perfect!
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 15:16 schrieb alison.pamment at stfc.ac.uk<mailto:alison.pamment at stfc.ac.uk>:
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<mailto:j.m.gregory at reading.ac.uk>
Cc: Michael.Buchwitz at iup.physik.uni-bremen.de<mailto:Michael.Buchwitz at iup.physik.uni-bremen.de>; Veronika.Eyring at dlr.de<mailto: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<
http://www.iup.uni-bremen.de/%7Emreuter>
____________________________________________________________________
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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