[CF-metadata] mixing ratio

From: Philip J. Cameronsmith1 <cameronsmith1>
Date: Tue, 4 Nov 2008 08:42:58 -0800 (PST)

On Tue, 4 Nov 2008, Pamment, JA (Alison) wrote:

> Dear Martin, Heinke and Jonathan,
>
> Martin wrote:
>
>>>> 'water_vapor_mixing_ratio'
>>>> water vapor mixing ratio of a parcel of moist air is the ratio of
>> the
>>>> mass of water vapor to the mass of dry air.
>>> I think there is agreement that the existing standard name
>> humidity_mixing_ratio has the right
>>> definition, but that water_vapor_mixing_ratio would be more
>> self-explanatory. Therefore I will
>>> add the name water_vapor_mixing_ratio and make humidity_mixing_ratio
>> into an alias.
>>
>> Now I am really puzzled! For all chemical constituents we went a
>> long way to make the distinction between
>> mass_fraction_of_ and mole_fraction_of_ (see my mail to Philip
> of
>> this morning)
>>
>> Why shouldn't this be the case for water vapour, which can also be
>> seen as a chemical constituent???
>>
>> The "mixing_ratio" label doesn't allow to infer the canonical units.
>>
>> So, my suggestion would be
>>
>> mass_fraction_of_water_vapour_in_air
>>
>> and if you insist on humidity, then we would need an alias to
>>
>> mass_fraction_of_humidity_in_air
>
> This raises a couple of points. Firstly, as Jonathan said,
>
>> I think the mass fraction of water vapor in air would be the ratio of
> mass of water vapour
>> to mass of moist air. That's not quite the same. Would you agree?
>
> I think Jonathan is correct because, unless stated otherwise, 'air'
> would be assumed to be moist.
>
> The name that currently exists in the table for this quantity is
> humidity_mixing_ratio, but I think that we are all agreed to use the
> term 'water_vapour' rather than 'humidity'. This would seem to leave us
> with two possible choices for this name: either
>
> 'water_vapour_mixing_ratio'
> which was agreed between Jonathan and Heinke, or
> 'mass_fraction_of_water_vapour_in_dry_air'
>
> which would be more consistent with treating water vapour as a chemical
> constituent, as well as a physical one. I think that Martin's point that
> water vapour can be regarded as a chemical constituent is a very fair
> one. 'Mixing ratio' is not a term that is widely used in standard names
> so changing this one name to 'mass_fraction' will not make it
> inconsistent with any other group of names. Personally, I could live
> with either solution so I am happy to go with the majority view.
>
> Best wishes,
> Alison

Hi Alison,

I vote for 'mass_fraction_of_water_vapour_in_dry_air'. I think it
is clearer and more consistent, even though it is longer.

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
------------------------------------------------------------------------
Received on Tue Nov 04 2008 - 09:42:58 GMT