[CF-metadata] mixing ratio

From: Jonathan Gregory <j.m.gregory>
Date: Thu, 6 Nov 2008 16:08:29 +0000

Dear Alison

Ah, now I see. I found that confusing, though. If I read "fraction of A in B"
I'd assume that A is a subset of B e.g. I assume that mass fraction of fat
in cream means fat/cream, not fat/(cream-fat), and mole fraction of nitrogen
in air means nitrogen/air. If I read "mass fraction of fat in fat-free yoghurt"
I would be confused in the same way as I was about "mass fraction of water
vapor in dry air".

I agree that your definition is exactly what humidity mixing ratio means.
Here's a more explicit statement of what it means:
  mass_ratio_of_water_vapor_to_dry_air_in_air
But would it be acceptable to stick with humidity_mixing_ratio and regard it
as an exceptional name? It does seem like a good idea to avoid "mass mixing
ratio" in general as it is not consistently used regarding the denominator.

> We already have mole_fraction_of_water_vapor_in_air in the table and we
> could certainly also introduce mass_fraction_of_water_vapor_in_air
> which, using the same definitions of A and B as before, would mean
> simply A/B.

Yes. If we need that quantity, it would be the logical name.

> If we use 'ambient air' instead of just 'air' in this case
> then we ought really to change all the mass|mole_fraction_of_X_in_air
> names to be consistent. That would mean creating 104 aliases.
> Personally, I'm not convinced of the need for this. ...
> So I would vote for continuing to use 'air' to mean moist/ambient air
> and 'dry_air' to mean air excluding water vapor.

OK.

Best wishes

Jonathan
Received on Thu Nov 06 2008 - 09:08:29 GMT