Hello Mahalo, Charlie,
My gut feeling was "it shouldn't", but I then thought "why not?" after
I couldn't think of any counter examples hwich would cause problems.
Section 7.3 doesn't disallow it, I think, and I don't think there will
be any conflict or ambiguity arising from its use. Appendix A would
need to be updated and perhaps some text in 7.3 highlighting that it
is OK, clarifying that the variable (the time coordinate in your
example) "defines its own cells"?
This is similar to the recent (ongoing) thread on allowing a
coordinate variable to have an ancillary_variables attribute.
Does that still make sense?
All the best,
David
---- Original message from Charlie Zender (05PM 31 May 15)
> Date: Sun, 31 May 2015 17:17:35 -0700
> From: Charlie Zender <zender at uci.edu>
> To: CF Metadata Mail List <cf-metadata at cgd.ucar.edu>
> Subject: [CF-metadata] Are cell_methods attributes OK for coordinate
> variables?
> User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101
> Thunderbird/31.4.0
>
> Aloha CFers,
>
> Is it correct to add a cell_methods = "time: mean" attribute to the
> time coordinate when the coordinate is averaged over time?
> NCO's ncra does this (though the NERC CF checker doesn't like it).
> It's clear from the CF docs that ncra time-averaging a variable like
> wind(time) from an array to a degenerate (size 1) array should
> add a cell_methods = "time: mean" attribute to wind.
> Yet should it add cell_methods to the time coordinate itself?
>
> My take is that it should. The time_bounds variable, if any,
> will show the original extent of the temporal range, and the time
> coordinate value contains the mean of the original range.
> Yet an NCO user is making a good case that cell_methods are only
> for non-coordinate variables. His point is that many variables with
> different cell_methods can all contain the same coordinate, so that
> the coordinate should not have cell_methods. My response is that
> cell_methods refers to the bounds variable of the coordinate, not
> the coordinate values themselves.
>
> Is the question clear? If not, I can supply CDL...
>
> Mahalo,
> Charlie
>
> p.s. the CF list archives on the CF homepage poinst to
> http://mailman.cgd.ucar.edu/pipermail/cf-metadata
> and that URL currently (and for the past ~week) yields this error:
> The requested URL /pipermail/cf-metadata/ was not found on this server.
> --
> Charlie Zender, Earth System Sci. & Computer Sci.
> University of California, Irvine 949-891-2429 )'(
> _______________________________________________
> CF-metadata mailing list
> CF-metadata at cgd.ucar.edu
> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
--
David Hassell
National Centre for Atmospheric Science (NCAS)
Department of Meteorology, University of Reading,
Earley Gate, PO Box 243,
Reading RG6 6BB, U.K.
Tel : +44 118 3785613
E-mail: d.c.hassell at reading.ac.uk
Received on Mon Jun 01 2015 - 03:35:40 BST
