[CF-metadata] Use of Standard Names and Coordinate Variables (relevant to the aerosol discussion)

From: Bryan Lawrence <b.n.lawrence>
Date: Wed, 27 Sep 2006 08:25:30 +0100

hi Folks

The discussion of aerosol standard names raises some issues. I think
things are going along just fine, but in the longer term there are some
problems looming ...

Putting things off into coordinate variables. This is in principle
fine ... but when one comes to finding particular variables amongst huge
numbers of files, then the more thing we put off into coordinate
variables the harder discovery becomes.

In practice we start having to build "discovery standard names" which
have all the semantics (forget the syntax for now) of the coordinate
variables, the cell measures etc. People do look for pm10 for example,
it is a common search term, and it has meaning as a name to a huge
community, including the entire pollution world. And what will we put on
the plot title? This new "compound/discovery" name, not the standard
name.

I think we have to be pragmatic and identify some "coordinates" which
are also in in such common usage that they really are names.

So in the following discussion:

> PM10 is particulate matter with an aerodynamic diameter of up to 10 ?m,
> i.e. the fine and coarse particle fractions combined.

> > Use of dimensions:
> >
> > * Some of the names have numerical values in them. This is not in keeping with
> > usual practice in standard names. For instance, we do not have standard names
> > for surface air temperature at 1.5 m or 2 m height. Instead, we use coordinates
> > for independent variables. In names like these:
> > mole_fraction_of_CO_with_lifetime_of_25_days_in_air
> > pm10_aerosol_ambient_optical_depth_at_550_nm
> > mass_fraction_of_pm10_aerosol_at_50_percent_relative_humidity_in_air
> > I think the lifetime, particle radius, wavelength and relative humidity should
> > be coordinates (probably scalar coordinate variables), rather than being in the
> > standard name. This requires standard names to be defined for the independent
> > variables you need.

I disagree with this suggestion. Temperature at 1.5m is an obvious
coordinate thing, but pm10 is not a coordinate thing, so I don't think
particle radius should disappear off into ancillary information, it
really is integral to the name (as Christiane says, it even appears in
legislation). I'm not even convinced by the argument that wavelength and
RH should disappear off into coordinate variables either.

What is the use case for having them in coordinate variables? Do we ever
expect people to use these variables as coordinates per se? (We can
imagine it in the temperature case). We have to look past whether these
look like numbers and ask: are they labels? or are they things which
have properties like coordinates?

Bryan
Received on Wed Sep 27 2006 - 01:25:30 BST