Re: [cf-pointobsconvention] Should Z Coordinates be required?

• To: cf-pointobsconvention@xxxxxxxxxxxxxxxx
• Subject: Re: [cf-pointobsconvention] Should Z Coordinates be required?
• From: Jonathan Gregory <j.m.gregory@xxxxxxxxxxxxx>
• Date: Tue, 25 Sep 2007 16:59:52 +0100

Dear John G

>Also I don't think we should confuse the z of the quantity being measured with 
the z
>of the platform which is measuring it.

I don't think we are confusing those two values.

For a precipitation flux or a pressure at mean sea level (calculated by
correcting surface pressure to sea level) there a station altitude, of course,
but that is not the "altitude" of the quantity measured. Precipitation is by
definition a surface quantity, and pressure at mean sea level is at mean sea
level, so doesn't have an altitude. I would regard the altitude in these cases
as useful ancillary metadata, but not a coordinate. For temperature measured in
a met enclosure, the Z coordinate would be height (=1.5 m or 2 m). The
station still has the same altitude as for the precipitation measurement, but
you would record the height, not the altitude, as the Z coord. (At least, in
all the model data archived at PCMDI, surface air temperature has a Z coord
of height.) I think that shows that the altitude of the station is *not* the Z
of the precipitation or the sea-level pressure value. However, it is definitely
useful to know and should be recorded.

Best wishes

Jonathan G

• Follow-Ups:
  • Re: [cf-pointobsconvention] Should Z Coordinates be required?
    • From: John Caron