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" <[email protected]> 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, [email protected], Lawrence Livermore National Lab. > ----------------------------------------------------------------------- > > >> -----Original Message----- >> From: Jonathan Wrotny [mailto:[email protected]] >> Sent: Thursday, October 03, 2013 12:40 PM >> To: Cameron-smith, Philip >> Cc: Jonathan Gregory; [email protected] >> 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, [email protected], Lawrence Livermore National >>> Lab. >>> ---------------------------------------------------------------------- >>> - >>> >>> >>>> -----Original Message----- >>>> From: CF-metadata [mailto:[email protected]] On >> Behalf >>>> Of Jonathan Gregory >>>> Sent: Thursday, October 03, 2013 9:35 AM >>>> To: [email protected] >>>> 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 <[email protected]> ----- >>>> >>>>> Date: Wed, 2 Oct 2013 11:26:27 -0400 >>>>> From: Jonathan Wrotny <[email protected]> >>>>> User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:17.0) Gecko/20130801 >>>>> Thunderbird/17.0.8 >>>>> To: Jonathan Gregory <[email protected]>, "cf- >>>> [email protected]" >>>>> <[email protected]> >>>>> 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 >>>>>> [email protected] >>>>>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata >>>> ----- End forwarded message ----- >>>> _______________________________________________ >>>> CF-metadata mailing list >>>> [email protected] >>>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata >>> _______________________________________________ >>> CF-metadata mailing list >>> [email protected] >>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > > _______________________________________________ > CF-metadata mailing list > [email protected] > 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 _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
