[CF-metadata] mixing ratio

[Philip J. Cameronsmith1]

On Thu, 6 Nov 2008, Jonathan Gregory wrote:

> Dear Christiane
>
>> Instead of 'moist' I would suggest 'ambient'. This would be consistent
>> with 'ambient' aerosol.
>
> Good idea.
>
>> In addition, the mass fraction of water vapor in dry air is not zero,
>> this is possible and used in models.
>
> What does it mean, then? I assume "dry air" means "air containing no water".
> Can it have a non-zero mass fraction of water vapour?
>
> Best wishes
>
> Jonathan

Hi Jonathan,

In this case I would consider 'dry air' to just be the denominator.  This 
has the advantage that concentrations of species won't change indirectly 
due to moist processes affecting the denominator.  Hence, 'the mass 
fraction of water vapor in dry air' is a perfectly reasonable quantity to 
use in a model, and can be non-zero.  Of course, this may not be the 
appropriate quantity for some calculations, but in that case 'the mass 
fraction of water vapor in dry air' is just what is needed to convert the 
mass fractions of all species in dry air to actual mass fractions :-).

Best wishes,

     Philip


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Dr Philip Cameron-Smith        Atmospheric, Earth, and Energy Division
pjc at llnl.gov                   Lawrence Livermore National Laboratory
+1 925 4236634                 7000 East Avenue, Livermore, CA94550, USA
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