Karl,
Thanks for the endorsement. We use the coord name "lev" because
several "generic" netCDF applications recognize this as a vertical
coordinate array. In programming our own applications we typically
use "zp" or "zplev". We also include another coord array "ilev" on
the histories, which is the same as lev, except its at the cell
interfaces rather than the midpoints (as reflected in the long_name).
Most fields are calculated at the midpoints, with a few exceptions,
such as geopotential height and electron density, which are calculated
on interfaces.
In publications, we sometimes use "ln(p0/p)" as a label for the
vertical axis of plots, with a brief explanation in the figure caption
or the text.
This coordinate is analogous to the upper part of the
atmosphere_hybrid_sigma_pressure_coordinate that is used by the
NCAR CAM model, where ground topography sigma is no longer in play.
We do not generally include ground effects because our model's
lbc is in the upper stratosphere (except indirectly via gravity
wave parameterization).
--Ben
>
>Dear Ben,
>
>Thanks for the very thorough proposal, which I endorse. I have a
>question concerning notation, however. I presume "lev" is the name of
>the variable you use when programming, but what do you use when you
>publish a paper for this quantity? If this quantity is normally
>referred to as zprime or zstar or xi or whatever in the literature, it
>would probably be more consistent with the other coordinate definitions
>if we replaced "lev" in your description with that commonly used symbol.
>
>Note that "var2", in the case of your model, would be set to "lev".
>
>If there is no conventional symbol for this coordinate, also let us know.
>
>Finally, is this the most general form of this coordinate? Is it a
>special case or closely related to any others used strato, meso,
>thermosphere models?
>
>Thanks very much for your interest in CF.
>
>regards,
>Karl
>
>Karl Taylor (taylor13 at llnl.gov)
>
>Ben Foster wrote:
>> 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
>>
>>
>>
>> -----------------------------------------------------------------------
>> 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
>> -----------------------------------------------------------------------
>>
>> _______________________________________________
>> CF-metadata mailing list
>> CF-metadata at cgd.ucar.edu
>> http://www.cgd.ucar.edu/mailman/listinfo/cf-metadata
>>
>
-----------------------------------------------------------------------
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
-----------------------------------------------------------------------
Received on Thu Mar 09 2006 - 10:14:50 GMT
