[CF-metadata] mixing ratio

From: Philip J. Cameronsmith1 <cameronsmith1>
Date: Thu, 6 Nov 2008 02:00:40 -0800 (PST)

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


------------------------------------------------------------------------
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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Received on Thu Nov 06 2008 - 03:00:40 GMT