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 -----
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Received on Fri Oct 04 2013 - 18:28:12 BST
