[CF-metadata] Question to Parametric Vertical Coordinates

From: Jonathan Gregory <j.m.gregory>
Date: Tue, 15 Oct 2019 17:31:42 +0000

Dear Daniel

> Does "Parametric Vertical Coordinates" mean that there is a mathematical
> function, which describes the relation between the relevant (auxiliary)
> coordinate variables and the parametric vertical coordinate?

In section 4.3.3, it means that the physical vertical coordinate z(k,j,i),
where i,j are indices of the horizontal dimensions and k of the vertical,
can be written as as a mathematical function
  z=f(V1(k)[,V2(k),...],H1([t,]j,i)[,H2([t,]j,i)...])
where V1,... depend only on level, and H1,H2,... depend only on horizontal
position (and perhaps on time). I think that describes all the cases of
Appendix D, but someone may correct me! The entries in App D describe the
physical vertical coordinate and how to compute it with the formula f.

> Speaking in terms of the example provided further below: Value of `depth` is
> a `f(time, lev, lat, lon)`, whereas `f` is a mathematical function with
> considerably less parameters than `depth` has values. Then `depth` is a
> parametric vertical coordinate.
>
> Formulated the other way arond: Is `depth` NOT a parametric vertical
> coordinate if its values are somehow set by hand (by a human), calculated by
> some nested if-clause, or by some iterative procedure?
>
> If `depth` is not a parametric vertical coordinate in this sense, am I
> allowed to use it in a CF-compliant file?

The depth variable in your example is a 4D auxiliary coordinate variable. It
is CF-compliant, but it's not a CF parametric vertical coordinate variable.

> Example:
>
> ...
> int lev(lev):
> lev:standard_name = "model_level_number" ;
> lev:long_name = "model_level_number" ;
> lev:positive = "down" ;
> lev:units = "1" ;
> double depth(time, lev, lat, lon);
> depth:long_name = "depth" ;
> depth:positive = "down" ;
> depth:standard_name = "depth" ;
> depth:units = "m" ;
> depth:axis = "Z" ;
> float some_data_variable(time, lev, lat, lon);
> some_data_variable:standard_name = "some_standard_name" ;
> some_data_variable:units = "some_unit" ;
> some_data_variable:coordinates = "depth"

Best wishes

Jonathan
Received on Tue Oct 15 2019 - 11:31:42 BST