[CF-metadata] mixing ratio

From: Jonathan Gregory <j.m.gregory>
Date: Mon, 24 Nov 2008 08:27:23 +0000

Dear Christiane

> Maybe I have missed the recent discussion, but to my understand, the
> mixing ratio is generally defined as
> x/(sum_of_all_components_including_x), which would mean in our case the
> humidity_mixing_ratio would be equivalent to
> mass_fraction_of_water_vapor_in_ambient_air.
> For example, on the web I found that the mole mixing ratio of N2 in air
> is 78%, which means that my definition of the mixing ration is applied.
> Could you please comment on this? At least a comment on the definition
> of humidity_mixing_ratio would be good.

I also had a look at the web, and my understanding is that the terms "mixing
ratio of X in air" and "mass fraction of X in air" are used effectively
interchangeably for all minor species X *except* water vapour. For water
vapour, the common terms are (I believe) humidity mixing ratio and specific
humidity. Specific humidity means
mass_fraction_of_water_vapor_in_ambient_air
=(water vapour)/(air including water vapour),
while humidity mixing ratio
=(water vapour)/(dry air)
Both specific_humidity and humidity_mixing_ratio are standard names at present
and I propose we keep them. For other X we could use different constructions.

Cheers

Jonathan
Received on Mon Nov 24 2008 - 01:27:23 GMT