[CF-metadata] mixing ratio

From: Jonathan Gregory <j.m.gregory>
Date: Thu, 6 Nov 2008 08:31:58 +0000

Dear Alison et al.

I wrote

> I think we could include both of these:
>
> > >'water_vapour_mixing_ratio'
> > >'mass_fraction_of_water_vapour_in_dry_air'
>
> They are different quantities, and people should use the one which describes
> their data.

That was wrong, sorry, I wasn't thinking.

Shouldn't the second option be
  mass_fraction_of_water_vapour_in_moist_air
or just
  mass_fraction_of_water_vapour_in_air
assuming that "air" means just as it comes i.e. not dry? The mass fraction
of water vapour in dry air is zero. I think
  mass_fraction_of_water_vapour_in_[moist_]air
  water_vapour_mixing_ratio
are two different quantities, which should have different standard names. If
A is the mass of water vapour and B is the mass of dry air, the mixing ratio
is A/B and the mass fraction is A/(A+B), I believe. I think the mass fraction
is what we use for other chemical constituents. If C is the mass of some other
species, the mass fraction of C in air is C/(A+B), because "air" would be
assumed to be ambient, including whatever moisture A it has.

Best wishes

Jonathan
Received on Thu Nov 06 2008 - 01:31:58 GMT