Dear all,
I would also like to support this proposal. And I thank Philip for his careful thinking.
>> If these were the only aspects to consider then I would be against the new std_name. However, there
>> are many more species than ozone, and ozone is the only one that I see expressed as equivalent thickness.
>> This means that we will surely end up wanting atmosphere_mole_content for other species, so it makes
>> sense to have it for ozone too. For me, this tips the balance in favor of accepting the proposed std_name.
Wouldn't this even call for recommending the use of atmosphere_mole_content as preferred option? Since both quantities are essentially the same and both are reported in DU, it will be merely a naming thing in practice. The advantage being that it will be easier for outsiders to understand that an atmosphere_mole_content of ozone is the same concept as an atmosphere_mole_content of some other species, whereas this gets lost if the default for ozone is equivalent_thickness_at_stp_of_atmosphere_ozone_content while all other compounds use atmosphere_mole_content.
Should we even go as far as to deprecate the use of equivalent_thickness_at_stp_of_atmosphere_ozone_content?
Philip also raises a good point with respect to alias names: has it been stated clearly that they must refer to "exactly the same quantity"? I believe they should, because if we allow "trivial" unit conversions to count as aliases, then even "wavelength" and "frequency" could be considered of aliases, which surely no one would want.
Best regards,
Martin
Date: Thu, 6 Dec 2012 23:41:16 +0000
From: "Cameron-smith, Philip" <cameronsmith1 at llnl.gov>
To: "alison.pamment at stfc.ac.uk" <alison.pamment at stfc.ac.uk>,
"Christophe.Lerot at aeronomie.be" <Christophe.Lerot at aeronomie.be>
Cc: "victoria.bennett at stfc.ac.uk" <victoria.bennett at stfc.ac.uk>,
"cf-metadata at cgd.ucar.edu" <cf-metadata at cgd.ucar.edu>
Subject: Re: [CF-metadata] new standard name proposal for total ozone
in DU
Message-ID:
<298F51ABD432DA4288CE6B8C469A2AFC33857E at PRDEXMBX-04.the-lab.llnl.gov>
Content-Type: text/plain; charset="us-ascii"
Hi All,
After considerable thought, I do support addition of this std_name, but recommend that we add a comment to the description (as described below).
The problem is that
atmosphere_mole_content_of_ozone (proposed, units = moles/m2, typically expressed in DU)
and
equivalent_thickness_at_stp_of_atmosphere_ozone_content (already in CF, units = m, typically expressed in DU)
are essentially the same. Although they have nominally different units, the usual unit used in both cases is Dobson Units (DU). 1 DU was originally defined as 10 micrometers of ozone at STP (ie a unit of distance), but can equivalently defined as 446.2... micromoles/m2 (ie, related to 'moles/m2'), see
http://en.wikipedia.org/wiki/Dobson_unit. The conversion is trivially done through the ideal gas law.
A user putting ozone column data into CF is just as likely to use one std_name as the other, and use DU for the units in either case. It would be appropriate to compare the data directly (with no unit conversion if both are put in as DU).
Hence, different datasets may contain the same data using different std_names, which isn't ideal.
On the other hand, the official units are different, and we have a related issue where we have separate std_names for quantities in 'moles' and 'mass', which are often trivial to convert between in many cases.
If these were the only aspects to consider then I would be against the new std_name. However, there are many more species than ozone, and ozone is the only one that I see expressed as equivalent thickness. This means that we will surely end up wanting atmosphere_mole_content for other species, so it makes sense to have it for ozone too. For me, this tips the balance in favor of accepting the proposed std_name.
Unfortunately, I don't think we can mitigate the problems using an alias because the std_names have different official units.
Hence, I propose that we simply add a note at the end of the descriptions for atmosphere_mole_content_of_ozone and equivalent_thickness_at_stp_of_atmosphere_ozone_content alerting users to the existence of the other std_name:
"Note: Ozone columns can be stored in either equivalent_thickness_at_stp_of_atmosphere_ozone_content or atmosphere_mole_content_of_ozone."
Best wishes,
Philip
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Dr Philip Cameron-Smith, pjc at llnl.gov, Lawrence Livermore National Lab.
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Received on Fri Dec 07 2012 - 00:35:59 GMT
