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" <cameronsmi...@llnl.gov>
To: "alison.pamm...@stfc.ac.uk" <alison.pamm...@stfc.ac.uk>,
"christophe.le...@aeronomie.be" <christophe.le...@aeronomie.be>
Cc: "victoria.benn...@stfc.ac.uk" <victoria.benn...@stfc.ac.uk>,
"cf-metadata@cgd.ucar.edu" <cf-metadata@cgd.ucar.edu>
Subject: Re: [CF-metadata] new standard name proposal for total ozone
in DU
Message-ID:
<298f51abd432da4288ce6b8c469a2afc338...@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
-----------------------------------------------------------------------
Dr Philip Cameron-Smith, p...@llnl.gov, Lawrence Livermore National Lab.
-----------------------------------------------------------------------
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