Dear Jonathan Thanks for considering Philip's arguments. Your decision is well-reasoned and seems fine to me. It was useful to have the debate.
Best wishes Jonathan ----- Forwarded message from Jonathan Wrotny <[email protected]> ----- > > Dear Philip, > > Thanks for the message and your perspective on equivalence of > standard names. In reviewing the surface_temperature definition > again and thinking about the observational data product motivating > my original submission, I do agree with you that the intent of the > two quantities is the same and, thus, the surface_temperature > standard name will suffice for the datal product that I have > submitted. Namely, they both refer to the interface or skin > temperature of the land surface. For a model surface temperature, > this is the temperature of the surface exactly at the interface of > the land and atmosphere, while the land surface temperature inferred > from an infrared radiometer, for instance, is the effective > temperature of the land interface/skin and other possible > terrestrial features (e.g. snow, vegetation) at the surface. While > both the model and observed surface temperature will have there own > associated uncertainties, these two quantities are compared directly > in practice in the community. In other words, I think they would > pass the test proposed in your post... > > If I want to validate one dataset against another (model-model, model-obs, or > obs-obs), would I be comfortable doing a simple subtraction between the > variables in the two datasets (ie, without any sort of correction)?" If > the answer is "yes", then I consider the quantities to be comparable, and > they should have the same std_name. If the answer is "no" then they should > have different std_names. > > Related to this is another point...for the case of a remotely sensed > temperature over land, the temperature will be sensitive to the > penetration depth of the radiation used for the measurement. The > penetration depth of the infrared measurements, for example, varies > with surface type (e.g., soil, inland water, snow, ice), therefore > is is not practical to assign a particular depth to the remotely > sensed surface skin temperature measurements. This lack of > preciseness argues for not creating a unique standard name for the > observable land surface temperature. On the other hand, it is > possible to be more radiometrically precise with the sea surface > skin temperature inferred from an observation and this bears it out > in the sea_surface_skin_temperature definition. > > So, I would like to retract my proposal for the > land_surface_skin_temperature. I believe that the current standard > name of surface_temperature will work fine. > > Sincerely, > > Jonathan Wrotny > > On 10/4/2013 11:36 PM, Cameron-smith, Philip wrote: > >Hi John, > > > >I apologize for not being clear :-(, so thank you for asking :-). > > > >I think you are raising a couple of issues: > > > >1) Is it appropriate for an observation and a model variable to have the > >same std_name? > > > >This wasn't the point I was trying to discuss. So hopefully I can clarify > >my thoughts a bit. > > > >Consider the (hypothetical) case where there is a theoretical quantity (e.g. > >skin temperature), which is calculated as part of a PERFECT model, and is > >also measured by a PERFECT instrument. In that case, both the model and > >observational data should have the same std_name. > > > >Now consider the case where the model and/or instrument are NOT perfect > >(e.g., the model equations actually use the average temperature of the top > >20m of soil, or the instrument actually measures the air temperature 10m > >above the surface). > > > >The test I apply is: "If I want to validate one dataset against another > >(model-model, model-obs, or obs-obs), would I be comfortable doing a simple > >subtraction between the variables in the two datasets (ie, without any sort > >of correction)?" If the answer is "yes", then I consider the quantities > >to be comparable, and they should have the same std_name. If the answer is > >"no" then they should have different std_names. Hence, the question of > >whether the data is from models or observations is not relevant. > > > >For my imperfect example above I would say it fails the test. If I was > >faced with that situation I would want to apply corrections to account for > >the difference between an air temperature and a soil temperature below the > >surface. > > > >If we improve the quantities (modeled or measured), then at some point they > >become 'close enough' to pass the test. > > > >Now for the specific case at hand, would I directly compare the skin > >temperature in my model against a spectroscopic measurement of the skin > >temperature from space (which presumably includes assumptions about fitting > >a black body and accounting for atmospheric absorption)? My answer would > >be "yes", and hence my objection to the proposed std_name. > > > >As a side note, I believe the decision of which std_name is appropriate for > >a quantity is generally best made by the person who creates the data, > >because they understand their own model or instrument, and they can also > >make the decision at the time the CF file is being created. But this is > >getting into a separate issue. > > > >2) Why am I objecting to land_surface_skin_temperature when > >sea_surface_skin_temperature has already been accepted? > > > >There are many quirks and inconsistencies in CF, as you know ;-), mostly > >because we discuss std_names one at a time (so we don't always see the big > >picture). I don't recall discussing sea_surface_skin_temperature. Perhaps > >it was before I joined the mailing list, or I wasn't paying attention. It > >is also possible that someone at the time made the argument that the > >temperature 10-20 microns below the surface of the ocean is sufficiently > >physically distinct from the theoretical skin temperature. [Do we want to > >reopen this discussion?] > > > >If the experts on this mailing list speak up and say that the distinction > >between 10-20 microns depth and the infinitesimal skin is physically > >important in practice, then I shall drop my objections. I just note that > >the proposal description for land_surface_skin_temperature states that the > >distinction is not very important. > > > >Best wishes :-), > > > > Philip > > > >----------------------------------------------------------------------- > >Dr Philip Cameron-Smith, [email protected], Lawrence Livermore National Lab. > >----------------------------------------------------------------------- > > > > > > > >>-----Original Message----- > >>From: CF-metadata [mailto:[email protected]] On Behalf > >>Of John Graybeal > >>Sent: Friday, October 04, 2013 6:04 PM > >>To: CF Metadata List > >>Subject: Re: [CF-metadata] Surface temperatures > >> > >>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 > >_______________________________________________ > >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
