[CF-metadata] proposed new vertical coordinate

[Ben Foster]

To the CF conventions community:

Over the past 25 years or so the High Altitude Observatory at NCAR 
has developed a series of Thermospheric GCM's for use in upper atmosphere 
research. We save simulation results in netCDF history files, which are
read by post-processors and visualization software. 

We would like to conform to CF conventions, but are currently unable
to do so because our vertical dimension coordinate is not recognized.
The vertical coordinate is a log pressure scale, ln(p0/p), where p0 is
a standard reference pressure. The resulting coordinate array "lev"
is typically -17 at the lower boundary to +7 at the top in increments
of 0.5 or 0.25, corresponding to about 30 to 500 km. Pressure in mb can 
be calculated with p(k)=p0*exp(-lev(k)).

We would therefore like to propose a new dimensionless vertical coordinate
for the CF convention as follows:

double lev(lev) ;
                lev:long_name = "midpoint levels" ;
                lev:units = "" ;
                lev:positive = "up" ;
                lev:standard_name = "atmosphere_log_pressure_coordinate" ;
                lev:formula_terms = "p0: p0 lev: lev" ;
                lev:formula = "p(k) = p0 * exp(-lev(k))" ;

If this acceptable, a new definition would be added to the atmosphere 
dimensionless vertical coordinate definitions in Appendix D, as follows:

=========================================================================
Atmosphere log pressure coordinate

standard_name = "atmosphere_log_pressure_coordinate"

Definition:

p(k) = p0 * exp(-lev(k))

where p(k) is the pressure at gridpoint (k), p0 is a reference pressure,
and lev(k) is the dimensionless coordinate at vertical gridpoint (k).

The format for the formula_terms attribute is

formula_terms = "p0: var1 lev: var2"
=========================================================================

Thanks for your consideration,

--Ben Foster



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Ben Foster		      	High Altitude Observatory (HAO)
foster at ucar.edu			phone: 303-497-1595  fax: 303-497-1589  
Nat. Center for Atmos. Res.     P.O. Box 3000 Boulder CO 80307 USA
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