[CF-metadata] Dimensionless vertical coordinate values

From: Jonathan Gregory <j.m.gregory>
Date: Mon, 10 Sep 2012 09:41:40 +0100

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
Received on Mon Sep 10 2012 - 02:41:40 BST