Dear Randy
I don't think a coordinate variable can have a coordinate variable - that is
not a mechanism which CF describes (although it's conceivable). Could you not
"flatten" it by regarding both the brightness temperature and the wavelength
as coordinates of the data variable, by phrasing the definition appropriately?
I don't know how to look at the CF standard name table at the moment so I can't
check the existing definitions, but I wonder whether we really need "threshold"
standard names. As far as I know, the only one is air_temperature_threshold,
yet we have some other standard names that refer to different thresholds. I
think it would be OK to say "there is a threshold brightness temperature" and
record this threshold in a coordinate variable with a standard name of
brightness_temperature - I think that would be clear enough.
Best wishes
Jonathan
On Thu, Apr 24, 2014 at 11:21:16AM -0400, rhorne at excaliburlabs.com wrote:
> From: "rhorne at excaliburlabs.com" <rhorne at excaliburlabs.com>
> To: cf-metadata at cgd.ucar.edu
> Date: Thu, 24 Apr 2014 11:21:16 -0400
> Subject: [CF-metadata] can a coordinate variable have a coordinate variable
> ?
>
> Dear All:
>
> We (Gary Meehan and I) have been proposing some tropical cyclone related
> standard names in recent weeks.
>
> For several of the quantities, their value is a function of a specific
> threshold brightness temperature value at the top of atmosphere (i.e.
> toa_brightness_temperature)
>
> In one of tropical cyclone standard name related proposals
> (radius_of_tropical_cyclone_central_dense_overcast_region), we got feedback
> from Jonathan advocating the use of a "threshold" coordinate variable
> (i.e. air_temperature_threshold).
>
> The original definition inadvertently failed to mention that this is a
> brightness temperature rather than an air temperature, so the standard name
> " air_temperature_threshold" is not what is needed. We will need to propose
> a standard_name like "toa_brightness_temperature_threshold".
>
> Given this, the variable with standard_name of
> radius_of_tropical_cyclone_central_dense_overcast_region will have a
> coordinate variable whose standard_name is
> toa_brightness_temperature_threshold, and this coordinate variable will
> need a coordinate variable capturing the wavelength/frequency of the
> standard_name.
>
> The implication is that a coordinate variable has a coordinate variable.
> Is this ok ?
>
> I have included Jonathan's email below as a reference below.
>
> very respectfully,
>
> randy
>
> +++++++++++
>
>
> Dear Gary In your new definition, the threshold is not stated, and I
> agree that it better in principle. However it would be informative to
> record the threshold used, I imagine. This could be done like this: > The
> average radius of a central region of clouds in tropical > cyclones lacking
> well-defined eye features > which is computed by averaging the great circle
> distance in four > cardinal directions. The radius > in each direction is
> measured from the estimated storm center > position to a warm point that
> exceeds > a threshold temperature limit. The threshold applied should be
> recorded in a coordinate variable having the standard_name of
> air_temperature_threshold. It could be a scalar or a size-one coordinate
> variable. Best wishes Jonathan
>
>
>
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Received on Thu Apr 24 2014 - 10:22:59 BST
