Hi Andreas,
You have the standard_name for both levm and levi correct already,
"atmosphere_hybrid_sigma_pressure_coordinate". That is what indicates
which dimensionless vertical coordinate you are using.
I do not believe you need a standard_name for hyam, hybm, hyai, or hybi.
But I'm really pressing the limits of my knowledge on this part of the
CF specification. You might want to post this to the CF mailing list and
see if anyone there has any suggestions. If you're not already on the
list, there is a link to the mailing list from the CF "Discussion" page
(http://cf-pcmdi.llnl.gov/discussion).
Ethan
On 8/24/2010 3:37 AM, Andreas Hilboll wrote:
> Hi Ethan,
>
> thanks for your comments!
>
>> It does say that a "coordinate variable is associated with its
>> definition by the value of the standard_name [and formula_terms]
>> attributes". Which means you need a coordinate variable (i.e., a 1-D
>> variable whose name matches its dimension name) for each vertical
>> dimension, in your case "levm(levm)" and "levi(levi)".
>
> Got it. Which would then be the standard_name for levm / levi?
>
>> Best practice is to fill the vertical coordinate variables with
>> approximate pressure level values and provide separate 1-D variables for
>> the formula terms. This allows applications that don't understand
>> dimensionless vertical coordinates (or don't want to go through all the
>> calculations) to use the vertical coordinate variables as a "reasonable"
>> approximation of pressure levels.
>
> Okay, I see. Again, which standard name should I give the variables?
> CF1.4 only has air_pressure, but I would need something like
> air_pressure_at_interfaces / air_pressure_at_midpoints.
>
>> 2) It looks like you are using the a/b formula rather than the ap/b
>> formula which means you need a "p0" term in your formula_terms attribute.
>
> No, actually, I am using the ap/b formula. Thanks for pointing out the
> mistake.
>
>> 3) None of the netCDF libraries automatically calculate the pressure
>> values from dimensionless coordinates. The netCDF C library does not
>> include features to deal with CF. The CF side of things is left to a
>> separate library, libcf. However, I don't believe libcf currently
>> include handling of dimensionless coordinates. The netCDF Java library
>> includes capabilities to deal with various parts of the CF specification
>> including dimensionless coordinates. I'm not sure what other libraries
>> deal with CF dimensionless coordinates.
>
> Okay, I see. In the example I mentioned, there is the vertical dimension
> variable indeed filled with approximate pressure levels, which made me
> believe that it was actually nc calculating the data. Which was
> obviously a stupid thought, because the dimensions wouldn't match ...
> Thanks for clarifying this!
>
> Cheers,
>
> Andreas
