Dear Jonathan,
Thanks for clarifying.
The original source of the confusion was example 4.3, where the
dimensionless vertical coordinate is itself one of the formula terms.
Similarly for hybrid height (where the dimensionless vertical
coordinate isn't even dimensionless!)
I've been through this discussion with several people prior to bringing
it to this mailing list, and no one could provide a definitive answer on
the expected behaviour. But slowly we settled on the definition that you
have confirmed. So I think CF would benefit from a couple of
clarifications. Firstly in the written description in section 4.3.2
(dimensionless vertical coordinate), and the choice of example. And also
in appendix D, where the description of what constitutes the
dimensionless vertical coordinate is not consistent across schemes -
sometimes it's hidden inline within the term descriptions; other times
it's a distinct sentence of its own.
Should I create a trac ticket containing a proposed clarification?
Richard Hattersley AVD Iris Technical Lead
Met Office FitzRoy Road Exeter Devon EX1 3PB United Kingdom
Tel: +44 (0)1392 885702 Fax: +44 (0)1392 885681
Email: richard.hatters...@metoffice.gov.uk Website:
www.metoffice.gov.uk
-Original Message-
From: Jonathan Gregory [mailto:j.m.greg...@reading.ac.uk]
Sent: 10 September 2012 09:42
To: Hattersley, Richard
Cc: cf-metadata@cgd.ucar.edu
Subject: [CF-metadata] Dimensionless vertical coordinate values
Dear Richard
On Mon, Aug 20, 2012 at 05:05:52PM +0100, Hattersley, Richard wrote:
I'm glad you think the first example makes sense - it's the one that
makes most sense to me too! But I'm wondering if one *must* store
ap(z)/p0+b(z) (or a(k)+b(k) if that's the parameterisation
in use), or
if one could store something else and still be a valid CF file?
Yes, I think one *must* store ap(z)/p0+b(z) or a(k)+b(k) in z
because that's
what the standard_name and units of the vertical coordinate
indicate z to be.
In your example
float z(z) ;
z:standard_name =
atmosphere_hybrid_sigma_pressure_coordinate ;
z:units = 1 ;
z:formula_terms = ap: delta b: sigma ps:
surface_pressure ;
z:positive = down ;
z says it's the atmosphere_hybrid_sigma_pressure_coordinate.
I think that
ap is the pressure part of the
atmosphere_hybrid_sigma_pressure_coordinate and
b is the sigma part of the
atmosphere_hybrid_sigma_pressure_coordinate. Neither
of them alone is the
atmosphere_hybrid_sigma_pressure_coordinate, so the
standard_name would be wrong if you stored either of the
components in z.
Also, if you stored the pressure part (ap) in z, the units
would be wrong as
well; the units say z is dimensionless, but ap is in Pa.
If this is right, should we clarify the convention text is some way?
Best wishes
Jonathan
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