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
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>>>>
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>>
>
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Received on Mon Jun 17 2013 - 08:17:24 BST
