[CF-metadata] physical vs dimensional units

From: Jonathan Gregory <j.m.gregory>
Date: Wed, 13 Apr 2011 15:24:19 -0000

Dear Martin

> if this is the direction to take, then we will need several "expressed_as" standard_names for atmospheric chemistry. Typical example: volatile organic compounds are often "expressed as" mass mixing ratio based on either their molecular mass or in "grams C" which counts only the mass of the C atoms (because this is what counts in the sense that it ultimately produces CO2 at the end of the reaction chain). Hence, one would need things like
> "mass_mixing_ratio_of_ethane_in_air_expressed_as_carbon_mass" and many similar ones.

Yes, indeed, we have already started down this direction e.g. there is an
existing standard name
  mass_fraction_of_brox_expressed_as_bromine_in_air

> I do sympathize with people who prefer to read "nmol mol-1" on a plot rather than "1" (or "1.e-9" in this case).

Since nmol mol-1 is equal to 1e-9, there is no problem with using it as units
in a CF file. It is udunits-compliant. It could even be stated as the
canonical unit in the standard name table.

Best wishes

Jonathan
Received on Wed Apr 13 2011 - 09:24:19 BST