Dear all,
I think for any conceivable purposes land_surface_skin_temperature is
identical to surface_temperature. If not, the definition should explain
how they differ. Is there really an important difference between the
temperature representative of the top few micrometers and the
temperature of the top few molecules of the surface? I know in models
there isn't. Also, over land presumably some sensors are inferring
this temperature from radiation emitted by some combination of both
vegetation and bare ground. "upper boundary of the land" sounds like
bare ground to me, so maybe this should be clarified.
Rather than define land_surface_skin_temperature to maintain consistency
with sea_surface_skin_temperature, I would prefer to deprecate
sea_surface_skin_temperature in favor of surface_temperature. As
Jonathon G. recalled, there was some rather extensive discussion about
sea_surface_skin_temperature when it was proposed, which should be
reviewed before deciding to deprecate. [I can't remember it, and I
don't think I participated in that earlier discussion, but I can't see a
need for skin_temperature.]
Reading over the 3 standard names relevant to SST (surface_temperature,
sea_surface_temperature, sea_surface_skin_temperature) here are some
comments:
For *models*: In ice-free regions all three quantities are identical.
In sea-ice-covered (or partially sea-ice-covered) regions only
sea_surface_skin_temperature and sea_surface_temperature are identical
(although one might argue that sea_surface_skin_temperature should not
be defined under sea ice because longwave radiative fluxes are normally
neglected between the sea ice and ocean below.) Globally all three are
the same if cell_method="area: mean where ice_free_sea".
For *observations*: There is a difference between
sea_surface_skin_temperature and sea_surface_temperature. In addition
sea_surface_temperature is imprecise because it depends on the measuring
device (e.g., ship intake temp., bucket temp. ). In ice-free regions
sea_surface_skin_temperature should be nearly identical to
surface_temperature (How big can the difference be between a weighted
average of temperature over the top 10-20 micrometers of the ocean and
the temperature of the top few molecules of the ocean??). Onemight
argue that sea_surface_skin_temperature should not be defined under sea
ice because the radiometers used to measure it would not normally
penetrate the sea-ice. If so, then surface_temperature with a
cell_method="area: mean where ice_free_sea" would be the same as
"sea_surface_skin_temperature" and they both would undefined under sea
ice. They would, of course, differ from sea_surface_temperature.
My conclusion is that sea_surface_skin_temperature is not needed and
should be deprecated and for similar reasons
land_surface_skin_temperature should not be added. We need to retain
both sea_surface_temperature and surface_temperature.
best regards,
Karl
On 6/19/13 8:32 AM, Jonathan Wrotny wrote:
> Dear Jonathan G and John G,
>
> Thanks to both of you for your replies to the questions on land
> surface skin temperature. I do agree with Jonathan G's points and see
> how the land surface temperature is likely very similar in value to
> the surface (interface) temperature, but my opinion is that for
> consistency of names within the CF and to alleviate general confusion
> (e.g. the inevitable questions of why there is not a land surface skin
> temperature when there is one for the sea surface), its seems useful
> to add a standard name for land_surface_skin_temperature. I think
> having the analogue to the sea surface quantity is complementary. I
> realized, however, that my initial definition of land surface skin
> temperature was a little too specific in attempting to quantify the
> depth of the skin layer. My general impression is that the depth of
> the land skin layer is more variable and not as well quantified as the
> depth of the sea surface skin. Thus, I generalized the definition to
> emphasize that the skin temperature is a radiometric quantity and
> removed the reference to the skin depth. Here is my current proposal:
>
> Standard Name: land_surface_skin_temperature
>
> Definition:The land surface skin temperature is the aggregate
> temperature of the "skin" of the land surface, where the "skin" is the
> upper boundary of the land which emits infrared radiation directly to
> space through the atmosphere.
>
> Canonical Units:K
>
>
> Any comments are appreciated.
>
> Sincerely,
>
> Jonathan Wrotny
>
> On 6/17/2013 10:17 AM, John Graybeal wrote:
>> As I understand it, the reason for the introduction of the skin temperature (and other sea surface temperatures) is that originally sea_surface_temperature encompassed everything (in its 100 years of use) from a bucket somewhere in the first 10 meters, to a satellite measuring the first few millimeters. More precise names were needed.
>>
>> I expect a similar situation applies on land. Even if past practice may only penetrate the service 10 centimeters, that's noticeably different than a satellite measuring a few millimeters. If that's at all true, having the refined term makes sense to me.
>>
>> John
>>
>> On Jun 17, 2013, at 05:41, Jonathan Gregory<j.m.gregory at reading.ac.uk> wrote:
>>
>>> Dear Jonathan and Jim
>>>
>>> In my previous email, I was trying to explain why an interface temperature
>>> is a physical meaningful concept, which Jonathan asked about. This is actually
>>> an applicable concept in models, as I said, and it is the idea which I (at
>>> least) had in mind when the name was put in the standard name table. Like CF
>>> in general, the standard name table was originally created for the purpose of
>>> model metadata, and was later to extended to observations. This quantity is an
>>> idealisation, not an observable quantity.
>>>
>>> The heat capacity of a layer 12 micrometers thick is so small that I suppose
>>> there is practically no difference between the skin temperature and the
>>> interface temperature, on the timescales you're interested in. Is that correct,
>>> do you think? If so, it seems to me that it would be fine to use the existing
>>> name of surface_temperature for this quantity. You propose the new name on the
>>> analogy of the sea_surface_skin_temperature. The same argument would apply to
>>> that as well. I can't remember the reason why it was thought necessary to make
>>> a distinction between surface_temperature and sea_surface_skin_temperature,
>>> though I do recall quite a lot of discussion about it.
>>>
>>> It is also fine to introduce land_surface_skin_temperature as well, I would
>>> say. The data-writer has a choice. They could use surface_temperature if that
>>> is accurate enough, but if they wish to be more precise about what material
>>> layer it applies to, the skin temperature names could be used.
>>>
>>> Best wishes
>>>
>>> Jonathan
>>>
>>> 13/06/17 13:20:03 house
>>> On Fri, Jun 14, 2013 at 02:45:28PM -0400, Jonathan Wrotny wrote:
>>>> Date: Fri, 14 Jun 2013 14:45:28 -0400
>>>> From: Jonathan Wrotny<jwrotny at aer.com>
>>>> User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:17.0) Gecko/20130509
>>>> Thunderbird/17.0.6
>>>> To: Jim Biard<jim.biard at noaa.gov>
>>>> CC:"cf-metadata at cgd.ucar.edu List" <cf-metadata at cgd.ucar.edu>
>>>> Subject: Re: [CF-metadata] new standard name: land_surface_skin_temperature
>>>>
>>>> Dear Jim,
>>>>
>>>> Thanks for your comments. They all make sense to me and I'm on
>>>> board with your suggested definition. I'll just wait for others to
>>>> comment, if needed, then we can converge on a final definition.
>>>> Sincerely,
>>>>
>>>> Jonathan
>>>>
>>>> On 6/14/2013 2:11 PM, Jim Biard wrote:
>>>>> Jonathan,
>>>>>
>>>>> I still don't believe that the surface temperature concept that
>>>>> Jonathan Gregory has ever been what people were intending when
>>>>> they make the surface_temperature standard name, but I'll abide by
>>>>> whatever folks decide.
>>>>>
>>>>> On a different front, I don't think the definition of the standard
>>>>> name should include statements about technology used (measured by
>>>>> an infrared radiometer?). The definition should speak only to the
>>>>> measured quantity, without reference to the way in which you
>>>>> happen to be measuring it. Likewise, there is no need for the
>>>>> statement regarding variability of the quantity. Also, the
>>>>> surface in this name is not the lower boundary of the atmosphere.
>>>>> It is the upper boundary of the land. An non-volatile object in a
>>>>> hard vacuum has a surface skin temperature.
>>>>>
>>>>> Given all that, I'd suggest this for your definition:
>>>>>
>>>>> Standard Name: land_surface_skin_temperature
>>>>>
>>>>> Definition: The land surface skin temperature is the aggregate
>>>>> temperature of the "skin" of the land surface, which extends
>>>>> vertically approximately 12 micrometers below the land surface.
>>>>>
>>>>> If people really think it needs to be spelled out even further,
>>>>> add the sentence "The land surface is the upper boundary of the
>>>>> land."
>>>>>
>>>>> Grace and peace,
>>>>>
>>>>> Jim
>>>>>
>>>>> Jim Biard
>>>>> Research Scholar
>>>>> Cooperative Institute for Climate and Satellites<http://www.cicsnc.org/>
>>>>> Remote Sensing and Applications Division
>>>>> National Climatic Data Center<http://www.ncdc.noaa.gov/>
>>>>> 151 Patton Ave, Asheville, NC 28801-5001
>>>>>
>>>>> jim.biard at noaa.gov <mailto:jim.biard at noaa.gov>
>>>>> 828-271-4900
>>>>>
>>>>>
>>>>>
>>>>> Follow us onFacebook<https://www.facebook.com/cicsnc>!
>>>>>
>>>>> On Jun 14, 2013, at 1:54 PM, Jonathan Wrotny <jwrotny at aer.com
>>>>> <mailto:jwrotny at aer.com>> wrote:
>>>>>
>>>>>> Dear Jonathan Gregory,
>>>>>>
>>>>>> Thanks for your reply...this certainly helps to clear things up
>>>>>> for me. I now better understand the meaning of the
>>>>>> "surface_temperature" standard name with the temperature defined
>>>>>> by heat fluxes at an interface, and not based on an actual
>>>>>> medium.
>>>>>>
>>>>>> This also makes it obvious to me that my proposed standard name
>>>>>> "land_surface_skin_temperature" does not currently exist within
>>>>>> CF and could serve as an analogue to
>>>>>> "sea_surface_skin_temperature." To summarize, here is my
>>>>>> current proposal:
>>>>>>
>>>>>> Standard Name: land_surface_skin_temperature
>>>>>>
>>>>>> Definition:The surface called "surface" means the lower boundary
>>>>>> of the atmosphere. The land surface skin temperature is the
>>>>>> temperature measured by an infrared radiometer, but measurements
>>>>>> from microwave radiometers operating at GHz wavelengths also
>>>>>> exist. It represents the aggregate temperature of the skin
>>>>>> surface where ?skin? means the surface medium viewed by a sensor
>>>>>> to a vertical depth of approximately 12 micrometers.
>>>>>>
>>>>>> Measurements of this quantity are subject to a large potential
>>>>>> diurnal cycle which is primarily due to the balance between
>>>>>> heating during the day by solar radiation and continual cooling
>>>>>> from terrestrial (long-wave) radiation emitted by the skin
>>>>>> surface.
>>>>>>
>>>>>> Canonical Units:K
>>>>>>
>>>>>>
>>>>>> Sincerely,
>>>>>>
>>>>>> Jonathan Wrotny
>>>>>>
>>>>>> On 6/14/2013 1:22 PM, Jonathan Gregory wrote:
>>>>>>> Dear Jonathan
>>>>>>>
>>>>>>> I defer to Roy about the various sea water temperature names.
>>>>>>>
>>>>>>> It is physically meaningful to have a temperature which doesn't relate to any
>>>>>>> material layer. If there is no matter associated with it, it must have zero
>>>>>>> heat capacity, so the temperature is determined by requiring an exact balance
>>>>>>> of heat fluxes. For this to be possible, the heat fluxes concerned must depend
>>>>>>> on the temperature, which of course they generally do. Obviously this is an
>>>>>>> idealisation, but a surface interface temperature of this kind really can
>>>>>>> exist in a model, although it's not an observational quantity. A model can
>>>>>>> obtain such a temperature by solving simultaneously for the heat fluxes that
>>>>>>> are balanced at the interface.
>>>>>>>
>>>>>>> Best wishes
>>>>>>>
>>>>>>> Jonathan G
>>>>>>> _______________________________________________
>>>>>>> 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 <mailto: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
>>
>>
>>
>> _______________________________________________
>> 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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <
http://mailman.cgd.ucar.edu/pipermail/cf-metadata/attachments/20130619/df621926/attachment-0001.html>
Received on Wed Jun 19 2013 - 14:44:11 BST
