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 imprecision 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
Received on Tue Jan 19 2016 - 09:39:38 GMT
