[cf-pointobsconvention] Z coordinate

I've been reading the comments on the z-coordinate and can see definite
value in having the z-coordinate in the data, and think that the GRIB2
format does give some guidance on this, but it also would need to be
examined properly... and I fear that may not be as trivial as first
thought. For example, 220 - Planetary Boundary Layer     from the table
4.5 could leave users to ask how the PBL has been determined: was it
from temperature inversion, aerosol content dropping or some other
method? Was it determined from a single sounding/profile (e.g.
radiosonde) or from averaging over time - this is important as a sonde
could give a different PBL height if it is in a convective plume or an
area of entrainment from the free troposphere.

As for whether the z-coordinate should be required or recommended I'd
tend to come down on the side of it being recommended and not required.
While it would be ideal to have (for example) both the Met. station
height above sea level and the height of each instrument above this base
height making it compulsory may either put people of from using the
format all together or could make it hard to get legacy data into
archives where such information may not be readily accessible and so the
archived data then has lots of redundant missing value entered in it.


Graham A Parton

BADC Helpdesk Manager

R25 1.117
Science and Technology Facilities Council
Rutherford Appleton Laboratory
Harwell Science and Innovation Campus
OX11 0QX

Tel:  +44 (0) 1235 446432
Fax: +44(0) 1235 446314

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