Philip, to be clear, are you saying one should, or should not, compare values from a model to observational values? We don't distinguish between them in CF names that I know of, so I'm assuming it's OK.... (And to Jonathon Wrotny's point: Considering a fundamental concept like "temperature of an observable feature" somehow different just by virtue of being in a model, is just way too big a Pandora's box to open up. In my humble opinion.)
For me, 'equivalent names' means equivalent _names_. If land_surface_skin temperature is equivalent to surface_temperature:cell_methods="area: mean where land", then sea_surface_skin_temperature must be equivalent to surface_temperature:cell_methods="area: mean where sea". And I bet I could find quite a few other 'equivalences' by using a cell method like "area: mean where land/sea".
Not only are such equivalences quite uncommon so far, to me it is not all that equivalent. (Perhaps that is my ocean background, where 'surface' is still a bit indeterminate -- rightly or wrongly!)
John
P.S. IIRC, sea_surface_temperature used to be the only sea surface temperature; other definitions were added because our view of the top of the ocean -- through satellites or models or thermometers -- was much more refined. So we needed more refined terms to make things comparable again.
On Oct 4, 2013, at 17:28, "Cameron-smith, Philip" <cameronsmith1 at llnl.gov> wrote:
> Hi Jonathan (Wrotny),
>
> The general practice of CF is that quantities that are 'equivalent', ie close enough that it is meaningful to take the difference between them, should have the same std_name (ie, they are both trying to calculate or measure the same physical quantity).
>
> IMHO, this provides huge value to users, since it tells them when they can, or shouldn't, compare two quantities (eg, compare the surface temperatures from a model dataset with satellite observations of surface temperatures). If 'equivalence' is treated too strictly, then no variable can ever be compared to another.
>
> Unfortunately, there is a grey zone between quantities are equivalent and quantities that are not, and then long discussions usually occur.
>
> From the description of the quantity you describe, it seems to me that land_surface_skin_temperature and surface_temperature:cell_methods="area: mean where land", should be deemed to be 'equivalent'.
>
> If you agree, then one advantage for you is that you don't have to do any more work on this email list ;-).
>
> Best wishes,
>
> Philip
>
>
>
> -----------------------------------------------------------------------
> Dr Philip Cameron-Smith, pjc at llnl.gov, Lawrence Livermore National Lab.
> -----------------------------------------------------------------------
>
>
>> -----Original Message-----
>> From: Jonathan Wrotny [mailto:jwrotny at aer.com]
>> Sent: Thursday, October 03, 2013 12:40 PM
>> To: Cameron-smith, Philip
>> Cc: Jonathan Gregory; cf-metadata at cgd.ucar.edu
>> Subject: Re: [CF-metadata] Surface temperatures
>>
>> Dear Philip,
>>
>> My take is that the land_surface_skin_temperature and the
>> surface_temperature are likely very close in value, since the
>> surface_temperature is an infinitesimally thin layer at the bottom level of the
>> atmosphere which interfaces with the land skin (soil) below - hence, the
>> definition stating that they can be taken to be equivalent.
>> The land_surface_skin_temperature proposal is motivated by a new
>> observational data product which is the radiating temperature of a very thin,
>> top layer of the land surface. This quantity does not currently exist in the CF
>> standard name set, but has an analogue in sea_surface_skin_temperature.
>> The surface_temperature name was added to CF because it is a standard
>> model variable, I believe. Someone please correct me if I am wrong, but the
>> radiating temperature of the Earth in models is often simply referrred to as
>> the "surface temperature," so I wanted to draw a connection between the
>> model quantity and the observable land_surface_skin_temperature in the
>> definition such that they are effectively the same thing. This seems to be
>> one of those situations where there are two quantities, one created for an
>> observed quantity and the other for a model quantity, but the two quantities
>> likely have very similar values. I guess the question is whether or not this is
>> permissible within CF.
>>
>> Sincerely,
>>
>> Jonathan Wrotny
>>
>> On 10/3/2013 1:30 PM, Cameron-smith, Philip wrote:
>>> Hi Jonathan (Wrotny), Jonathan (Gregory), et al.,
>>>
>>> I am a little surprised.
>>>
>>> It is explicitly stated in the proposed description that
>> land_surface_skin_temperature "can be taken to be equivalent to"
>> surface_temperature over land areas.
>>>
>>> In the description for surface_temperature, it indicates that it can apply to
>> just land using cell_methods. Indeed, in the CF convention, example 7.6
>> explicitly states this:
>>>
>>> Example 7.6. Mean surface temperature over land and sensible heat flux
>> averaged separately over land and sea.
>>> float surface_temperature(lat,lon);
>>> surface_temperature:cell_methods="area: mean where land";
>>>
>>> I also note that surface_temperature is already an alias for
>>> surface_temperature_where_land (which I think is deprecated)
>>>
>>> Why is a new std_name needed? What am I missing?
>>>
>>> It is true that there is a variable called sea_surface_skin_temperature, but
>> it appears that this was introduced for different reasons. Specifically, it looks
>> like sea_surface_temperature was created to refer to the water _near_ the
>> surface to distinguish it from the 'skin'. sea_surface_skin_temperature then
>> differs from surface_temperature because it refers to the interface under
>> sea-ice rather than above sea-ice.
>>>
>>> Best wishes, as always :-),
>>>
>>> Philip
>>>
>>> ----------------------------------------------------------------------
>>> - Dr Philip Cameron-Smith, pjc at llnl.gov, Lawrence Livermore National
>>> Lab.
>>> ----------------------------------------------------------------------
>>> -
>>>
>>>
>>>> -----Original Message-----
>>>> From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On
>> Behalf
>>>> Of Jonathan Gregory
>>>> Sent: Thursday, October 03, 2013 9:35 AM
>>>> To: cf-metadata at cgd.ucar.edu
>>>> Subject: Re: [CF-metadata] Surface temperatures
>>>>
>>>> Dear Jonathan
>>>>
>>>> The new proposal looks fine to me. Thanks. I see that you don't have
>>>> to define the thickness of the layer; instead, you are defining it
>>>> implicitly through the method of diagnosis. Others may have views, of
>> course.
>>>>
>>>> Cheers
>>>>
>>>> Jonathan
>>>>
>>>> ----- Forwarded message from Jonathan Wrotny <jwrotny at aer.com> -----
>>>>
>>>>> Date: Wed, 2 Oct 2013 11:26:27 -0400
>>>>> From: Jonathan Wrotny <jwrotny at aer.com>
>>>>> User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:17.0) Gecko/20130801
>>>>> Thunderbird/17.0.8
>>>>> To: Jonathan Gregory <j.m.gregory at reading.ac.uk>, "cf-
>>>> metadata at cgd.ucar.edu"
>>>>> <cf-metadata at cgd.ucar.edu>
>>>>> Subject: Re: [CF-metadata] Surface temperatures
>>>>>
>>>>> Dear Jonathan Gregory,
>>>>>
>>>>> I am getting back to this reply after a long time - sorry, I was
>>>>> pulled in a few different directions lately. Hopefully, it is
>>>>> possible to bring back to life a submission that I had made for the
>>>>> land_surface_skin_temperature.
>>>>>
>>>>> Revisiting my previous proposal and a few e-mails by Karl Taylor and
>>>>> Evan Manning, I have made some modifications to the definition of
>>>>> this standard name so that I can incorporate some suggestions by
>>>>> Karl and Evan. Here is my current proposal:
>>>>>
>>>>> Standard Name:land_surface_skin_temperature
>>>>>
>>>>> Definition:The land surface skin temperature is the temperature of a
>>>>> land point or the land portion of a region as inferred from infrared
>>>>> radiation emitted directly towards space through the atmosphere. Not
>>>>> all of the emitted surface radiation originates at the soil.Some may
>>>>> come from various terrestrial features (e.g., vegetation, rivers,
>>>>> lakes, ice, snow cover, man-made objects).Thus, the land surface
>>>>> skin temperature is the aggregate temperature of an effective layer
>>>>> which includes the soil and terrestrial features at the surface (if
>>>>> they occur).In models, the radiating temperature of the surface is
>>>>> usually the "surface_temperature", which then can be taken to be
>>>>> equivalent to land_surface_skin_temperature or sea_surface_skin
>>>>> temperature, depending on the underlying medium.
>>>>>
>>>>> Canonical Units:K
>>>>>
>>>>> Thanks for still considering this proposal. Sincerely,
>>>>>
>>>>> Jonathan Wrotny
>>>>>
>>>>> On 8/1/2013 12:56 PM, Jonathan Gregory wrote:
>>>>>> Dear all
>>>>>>
>>>>>> I agree with Karl than in CF standard names "land" means "non-sea",
>>>>>> whereas sea-ice is part of sea. Hence I would support adding
>>>>>> land_surface_skin_ temperature, for use by applications which
>>>>>> classify
>>>> locations as land or sea.
>>>>>> However I also agree with Evan that one can approach this more
>>>>>> generally, and therefore I would also support the addition of
>>>>>> surface_skin_temperature, with which an area-type could be
>>>>>> specified, if anyone wants to follow that approach (we only add
>>>>>> names when they
>>>> are needed).
>>>>>> The quotations that Evan made show that we need to change the
>>>>>> definitions where they mention "skin". This is because in these new
>>>>>> names "skin" is being given a more precise and practical meaning,
>>>>>> motivated by observational methods, whereas the
>> surface_temperature
>>>>>> names were introduced for models, in which the skin can be a
>>>>>> notional
>>>> and infinitesimally thin layer.
>>>>>> Best wishes
>>>>>>
>>>>>> Jonathan
>>>>>> _______________________________________________
>>>>>> CF-metadata mailing list
>>>>>> CF-metadata at cgd.ucar.edu
>>>>>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>>>> ----- End forwarded message -----
>>>> _______________________________________________
>>>> CF-metadata mailing list
>>>> CF-metadata at cgd.ucar.edu
>>>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>>> _______________________________________________
>>> CF-metadata mailing list
>>> CF-metadata at cgd.ucar.edu
>>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>
> _______________________________________________
> CF-metadata mailing list
> CF-metadata at cgd.ucar.edu
> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
------------------------------------
John Graybeal
Senior Data Manager, Metadata and Semantics
T +1 (408) 675-5545
F +1 (408) 616-1626
skype: graybealski
Marinexplore
920 Stewart Drive
Sunnyvale, CA
Received on Fri Oct 04 2013 - 19:03:32 BST
