Clarifying requirements for specific standard names.

[martinjuckes]

have reviewed the first half of the standard name list (a to m) and found the following coordinate constraints expressed:

(1) area_fraction: requires an area_type coordinate;

(2) atmosphere_lifting_condensation_level + 2 others: requires an original_air_pressure_of_lifted_parcel coordinate.

(3) Many "layer" quantities (e.g. dry_static_energy_content_of_atmosphere_layer): require vertical coordinate with bounds.

(4) change_in_energy_content_of_atmosphere_layer_due_to_change_in_sigma_coordinate_wrt_surface_pressure: must have a vertical coordinate variable (axis=Z)

(5) change_over_time_... and .._displacement: require bounds on time coordinate

(6) downwelling_photosynthetic_photon_radiance_in_sea_water and other radiance variables: direction must be specified, e.g. with coordinate of "zenith_angle".

(7) mass_concentration_of_pm..._ambient_aerosol_in_air (and mass_fraction_of_pm..): require air_temperature and relative_humidity

(8) isotropic_radiance_per_unit_wavelength_in_air (and other per_unit_wavelength varables): the definition is slightly ambiguous with the sentence "A coordinate variable for radiation wavelength should be given the standard name radiation_wavelength" which, taken literally, means the use of a wavelength coordinate is optional: should it be "A coordinate variable for radiation wavelength should be given with the standard name radiation_wavelength", making the wavelength coordinate required?

There are also a number of threshold variables.

[martinjuckes]

This issue is now being discussed in a trac ticket on the CF site: http://cf-trac.llnl.gov/trac/ticket/151