[CF-metadata] new standard name request for pH

From: Philip J. Cameronsmith1 <cameronsmith1>
Date: Mon, 4 May 2009 17:49:49 -0700 (PDT)

Hi,

For option (2), would it satisfy both the CF and ocean chemistry
communities to have the more descriptive standard name as Jonathan
suggests, and then put in the comments that 'This quantity is known as the
"total scale" for pH in the ocean chemistry community'? (and similarly
for the other pH quantities)

Best wishes,

      Philip


On Mon, 4 May 2009, John Graybeal wrote:

> Jonathan,
>
> No worries, I think we are zeroing in on the key points now. Though I don't
> yet know how ocean chemists will feel about the end results! But I
> appreciate the thorough analysis brought to the issue.
>
> In your option (1) (sea_water_pH universally), it isn't clear to me what
> other attribute would indicate the scale difference. I had understood that if
> the standard name and units were the same, CF users would assume the data
> could be exchanged, from a numerical standpoint anyway. If that is true, or
> if the specific attribute where this scale information must be entered, and
> the controlled vocabulary to use, is not specified, option (1) does not seem
> attractive. The likely outcome would be the attribute is unspecified or
> ambiguous, rendering the associated values useless to many potential users of
> the data.
>
> In case (2) (different geophysical quantities), we may be a little stuck. I
> quote from my own ocean chemist: "as an ocean chemist, I know EXACTLY what is
> meant by sea_water_pH_total_scale, and so do all the other ocean chemists."
> He believes other terminology will be opaque and ambiguous, and therefore
> essentially useless. As I understand the situation, the entire system of
> related chemistry in sea water is considered different depending on which
> scale is in use, so it is a pervasive concept in this domain, not simply an
> obscure name for this one measurement.
>
> Since I am unable to personally verify this last assertion with all those
> other ocean chemists, and you might not want to take my word for it anyway,
> it may be that you would like to verify this perspective with other experts
> in the domain? (I can provide some names offline if you would like to do
> that.) I think the reason to consider doing so in this case is that if there
> is indeed some ambiguity in the name you choose, then it may apply equally
> well in the future to a different scale, and this would be problematic.
>
> If, after such a discussion, or regardless of that point, you choose a name
> that seems more appropriate to you, we can always create our preferred name
> in another vocabulary and map it to yours. (Eventually I am sure the CF
> convention will support this technique in an embedded way. :->) So all is
> not lost, so long as the definition makes clear that the name you choose
> refers precisely to sea water pH total scale. Such an approach seems
> sufficiently usable to me, and we can bear the brunt of name translation for
> our cadre of ocean chemists.
>
> John
>
>
> On May 2, 2009, at 5:53 AM, Jonathan Gregory wrote:
>
>> Dear John
>>
>> Thanks for your thoughtful email. I follow the argument but in the end I do
>> not (yet) agree with the conclusion, that sea_water_pH_total_scale should
>> be a
>> standard name. I am sorry if you find that exasperating. As in previous
>> such
>> discussions, it is not because I am suggesting that you or your pH expert
>> are
>> mistaken about what terms are normally used and what they mean. My
>> difficulty
>> is that "total scale" is not informative to a general scientific
>> readership,
>> which CF standard names are designed to be.
>>
>> I've had a look at Zeebe and Wolf-Gladrow. Thanks for that reference.
>> Wikipedia summarises similar ideas. I also looked at a IUPAC document on
>> the
>> subject. It seems that problem of definition arises because pH is actually
>> impossible to measure, as defined! Hence the true value is somewhat
>> unknowable.
>> These different scales represent different methods of measurement and
>> estimation. I think we could take two views about that:
>>
>> * The different pH scales are actually trying to measure the same
>> geophysical
>> quantity. In that case the standard name should just be sea_water_pH. Then
>> the
>> scale is an aspect of the method of measurement, and should be recorded in
>> some other attribute. This is somewhat related to the other thread, about
>> quantities relating to the techniques of measurement.
>>
>> * The different pH scales are different geophysical quantities. In that
>> case
>> they need distinct standard names, and it ought to be possible to indicate
>> in some non-jargon way what the difference refers to, even though it
>> couldn't
>> be fully described in the name, so we still need a definition. Following
>> this
>> route, the total scale could be called
>> sea_water_pH_including_bisulfate_ions,
>> for instance. (A side-issue is a question of whether to call them bisulfate
>> or the IUPAC name of hydrogen_sulfate.)
>>
>> pH is a dimensionless quantity. It has no units. It's the logarithm of
>> a number which does have units, so the units of that quantity need to be
>> specified in the definition.
>>
>>> Yet the second
>>> sentence of the following statement does not hold true for pH, given
>>> the depths at which these measurements are being made:
>>>
>>> On Apr 30, 2009, at 9:22 AM, Jonathan Gregory wrote:
>>>> Boussinesq models (most ocean climate models are Boussinesq) treat
>>>> density
>>>> as constant 1000 kg m-3 except in the computation of pressure
>>>> gradients, where
>>>> it matters to the dynamics. Therefore in dealing with concentrations
>>>> of
>>>> tracers, per kg and per litre are identical and to choose one or the
>>>> other
>>>> would be arbitrary and hence unhelpful for data exchange.
>>
>> Actually this is a digression now, since all the quantities concerned are
>> logs of mol per kg. However, I maintain the above is a correct statement
>> about
>> ocean *models*. I did not say it's a correct statement about nature! It is
>> not, as you point out. However, Boussinesq models are only approximate. In
>> such models, that distinction could not be made. No-one has yet requested
>> pH for an ocean model, but I expect it will come up sometime.
>>
>> Best wishes
>>
>> Jonathan
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>
>
> --------
> John Graybeal <mailto:graybeal at mbari.org> -- 831-775-1956
> Monterey Bay Aquarium Research Institute
> Marine Metadata Interoperability Project: http:// marinemetadata.org
>
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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
------------------------------------------------------------------------
Received on Mon May 04 2009 - 18:49:49 BST