Let's pull in some existing surface temperature fields from the
standard name table.
surface_temperature
alias: surface_temperature_where_land
alias: surface_temperature_where_open_sea
alias: surface_temperature_where_snow
The surface called "surface" means the lower boundary of the
atmosphere. The surface temperature is the temperature at the
interface, not the bulk temperature of the medium above or below.
Unless indicated in the cell_methods attribute, a quantity is assumed
to apply to the whole area of each horizontal grid box. Previously,
the qualifier where_type was used to specify that the quantity applies
only to the part of the grid box of the named type. Names containing
the where_type qualifier are deprecated and newly created data should
use the cell_methods attribute to indicate the horizontal area to
which the quantity applies.
temperature_in_surface_snow
alias: snow_temperature
"Temperature in surface snow" is the bulk temperature of the snow, not
the surface (skin) temperature. The surface called "surface" means the
lower boundary of the atmosphere.
sea_ice_surface_temperature
The surface temperature is the (skin) temperature at the interface,
not the bulk temperature of the medium above or below. "Sea ice
surface temperature" is the temperature that exists at the interface
of sea ice and an overlying medium which may be air or snow. In areas
of snow covered sea ice, sea_ice_surface_temperature is not the same
as the quantity with standard name surface_temperature.
sea_surface_temperature
Sea surface temperature is usually abbreviated as "SST". It is the
temperature of sea water near the surface (including the part under
sea-ice, if any), and not the skin temperature, whose standard name is
surface_temperature. For the temperature of sea water at a particular
depth or layer, a data variable of sea_water_temperature with a
vertical coordinate axis should be used.
sea_surface_skin_temperature
The surface called "surface" means the lower boundary of the
atmosphere. The sea surface skin temperature is the temperature
measured by an infrared radiometer typically operating at wavelengths
in the range 3.7 - 12 micrometers. It represents the temperature
within the conductive diffusion-dominated sub-layer at a depth of
approximately 10 - 20 micrometers below the air-sea interface.
Measurements of this quantity are subject to a large potential diurnal
cycle including cool skin layer effects (especially at night under
clear skies and low wind speed conditions) and warm layer effects in
the daytime.
There seem to be different approaches implied. The comment in
surface_temperature about the old "where" aliases implies that we
should add "surface_skin_temperature" and encourage the use of cell
methods as needed.
I'm not so sure about how universal the meaning of "land" is. I've
used the MODIS MYD11C3 product. This provides land surface
temperature and land surface emissivity. No values are provided for
"marine" environments ... but no values are provided for ice or snow
covered environments either.
Some detailed comments about the latest proposed definition:
> 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 from the surface to space, without being absorbed by the atmosphere.
We should probably skip the stuff about space and the atmosphere. It
is equally a surface skin temperature
if it is measured from an airborne instrument or even a fixed
instrument a few meters above the surface.
The sea_surface_skin_temperature definition above goes into more
detail about being measured by a radiometer and what wavelengths are
typically used. I don't feel strongly about whether or not this type
of info is included but if we do go forward with 2 distinct fields
they probably should be consistent.
> Not all of the emitted surface radiation originates at the soil. Some comes from various terrestrial features (e.g., vegetation, rivers, lakes, ice, snow cover). 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 ocean_surface_skin temperature, depending on the underlying medium.
ocean_surface_temperature is a typo for sea_surface_temperature.
Currently we have these "surface_temperature"s:
surface_temperature
sea_surface_temperature
sea_ice_surface_temperature
Currently we have these "skin_temperature"s:
sea_surface_skin_temperature
There is no parallelism and adding land_surface_skin_temperature but
not surface_skin_temperature or sea_ice_surface_skin_temperature would
make it less parallel.
Personally, I support the idea that marine environments are unique, so
I like having a special "sea" category. But for everything else and for
situations where the marine distinction is not important, there should
be just a generic temperature. Cell methods or other CF mechanisms
can be used to specify what is measured. I'm undecided on how
special sea_ice is.
Counterproposal: Add surface_skin_temperature. Either add
sea_ice_surface_skin_temperature or deprecate
sea_ice_surface_temperature.
-- Evan
> From: Karl Taylor <taylor13 at llnl.gov>
> To: cf-metadata at cgd.ucar.edu
> Cc:
> Date: Wed, 17 Jul 2013 17:22:39 -0700
> Subject: Re: [CF-metadata] new standard name: land_surface_skin_temperature
> Dear all,
>
> I think the common meaning of "land" in climate models and in climate observations distinguishes "terrestrial" regions from "marine" regions. Thus, we have terrestrial plants, terrestrial water storage, terrestrial water fluxes, terrestrial glaciers (which seems a bit redundant), etc., and all of these comprise the "land" surface. Thus, in CF, I think "land" should include all it's components: vegetation, lakes, puddles, snow, glacial ice, etc. Sea ice, on the other hand, belongs to the marine environment and should be considered "sea".
>
> The above division fits nicely into how most models treat these two very different regions. Usually sea ice is part of the ocean model (or closely coupled to it, since the ocean can move sea ice around), and the "land model" can include all the land components, from vegetation to snow.
>
> I therefore think we should avoid terms as "nonsea", as that would be identical to "land".
>
> I agree that there seems to be a consensus that we adopt a new standard name -- land_surface_skin_temperature .
>
> To help users understand that it is likely to be a measure of the same thing as "surface_temperature", at least in models, I would modify the proposed definition along the following lines:
>
> 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 from the surface to space, without being absorbed by the atmosphere. Not all of the emitted surface radiation originates at the soil. Some comes from various terrestrial features (e.g., vegetation, rivers, lakes, ice, snow cover). 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 ocean_surface_skin temperature, depending on the underlying medium.
>
> I would also add this last sentence to the definition of "sea_surface_skin_temperature".
>
> Best regards,
> Karl
>
> On 7/16/13 10:00 AM, Evan Manning wrote:
>
> Jim,
>
> We're only half disagreeing. When there is a lake (or ice/snow?) on top of the land, you are talking about the radiative surface at the bottom of the atmosphere, not the top of the dirt. If I understand correctly, you only make a special case for designated oceans.
>
> So a more precise name might be "nonsea_surface_skin_temperature".
>
> Then if we have 50/50 land & lake with T=310 and 290:
> nonsea_surface_skin_temperature=300
> sea_surface_skin_temperature=(fill value)
> But 50/50 land & sea with T=310 and 290:
> nonsea_surface_skin_temperature=310
> sea_surface_skin_temperature=290
>
> Ice on land would presumably be counted as land but sea ice could still be counted as either land or sea with this terminology.
>
> so if we have 4 equal portions
> 1/4 non-ice-covered non-sea (land/lake/vegetation/whatever) T=290
> 1/4 ice-covered non-sea T=270
> 1/4 non ice-covered sea T=280
> 1/4 ice-covered sea T=260
>
> Then either we count sea ice as sea:
> nonsea_surface_skin_temperature=280 (men of 270 and 290)
> sea_surface_skin_temperature=270 (mean of 260 and 280)
> Or sea ice is not sea:
> nonsea_surface_skin_temperature=273.3 (men of 260, 270 and 290)
> sea_surface_skin_temperature=280
>
> -- Evan
>
> On Tue, Jul 16, 2013 at 9:36 AM, Jim Biard <jim.biard at noaa.gov> wrote:
>>
>> Evan,
>>
>> I'm afraid I have to disagree. I'm working with the MODIS and VIIRS Land Surface Temperature products right now, and they are attempting to report the temperatures of the soil/rock/plants/water/etc themselves. The sea surface is masked off, but temperature for water such as lakes and rivers (and puddles) is reported. The emissivities of the various surface constituents are used in the algorithms that generate the products. The top surface of the land is definitely what is of interest. To give one example, the products are used in drought studies, where they are used to try and determine how wet the soil is.
>>
>> Grace and peace,
>>
>> Jim
>>
>> Jim Biard
>> Research Scholar
>> Cooperative Institute for Climate and Satellites
>> Remote Sensing and Applications Division
>> National Climatic Data Center
>> 151 Patton Ave, Asheville, NC 28801-5001
>>
>> jim.biard at noaa.gov
>> 828-271-4900
>>
>>
>>
>> Follow us on Facebook!
>>
>> On Jul 16, 2013, at 11:59 AM, Evan Manning <Evan.M.Manning at jpl.nasa.gov> wrote:
>>
>> The rewording specifies that puddles are "land". What about ponds?
>> lakes? rivers? great lakes? Oceans?
>>
>> What if we have a grid square that is 50% land at 310 K and 50% ocean at 290 K?
>> Would it be correct to have these two variables associated with it:
>> sea_surface_skin_temperature=290
>> land_surface_skin_temperature=310 (i.e. T of only the non-sea portion)
>> or:
>> sea_surface_skin_temperature=290
>> land_surface_skin_temperature=300 (i.e. mean T of land & sea portions)
>>
>> How does that change if instead of being 50% ocean it is 50% lakes & rivers?
>> Or lots and lots of puddles?
>>
>> I think what we're interested in is not so much the top surface of the
>> land as the
>> lower boundary of the atmosphere. So I like "surface_skin_temperature", which
>> could then be used with a dimension for surface categories.
>>
>> -- Evan
>>
>> About a month ago, I submitted a new standard name for the "land_surface_skin_temperature." While I think the consensus is now that this new name seems acceptable for inclusion in the CF database, there were some comments and suggestions by various people who pointed out that the proposed definition for this quantity could use some more clarification and other comments which pointed out similarities to the current name "surface_temperature." I've attempted to address both of these concerns by adding another line to the definition which better defines what the "land_surface_skin" is. My hope is that this clears up some uncertainty about this quantity (e.g. it is not simply the bare land surface but also includes various media above the land surface) and also illustrates that it is not the same thing as the "surface_temperature" quantity (which I understand as idealized, infinitesimally thin interface temperature between the air and land/sea and not the observable quantity that the "land_surface_skin_tem
perature" proposes to be).
>>
>> With this is mind, here is my latest attempt at this new name/definition:
>>
>> Standard Name: land_surface_skin_temperature
>>
>>
>>
>> Definition: The land surface skin temperature is the aggregate temperature of the ?land surface skin,? which is the portion of the land surface which emits infrared radiation directly to space through the atmosphere. The ?land surface skin? is defined as an effective layer which includes the upper boundary of the land combined with additional layers which may cover the upper land boundary (e.g. vegetation, puddles, snow, ice, man-made objects).
>>
>>
>>
>> Canonical Units: K
>>
>>
>> Sincerely,
>>
>> Jonathan
>>
>> On 6/20/2013 7:56 AM, Jonathan Gregory wrote:
>>
>> Dear Karl
>>
>> Like Roy, I don't think we should deprecate sea_surface_skin_temperature.
>> Although I cannot remember the arguments - which must be apparent in the
>> mailing list archive - I do recall that it was a careful and long discussion
>> with Craig which led to the introduction of the various SST names.
>>
>> Therefore adding land_surface_skin_temperature seems fine to me if there is
>> a need to be precise about this as an observable quantity, which relates
>> to a particular layer, even though it's very thin. The definition should note
>> that if this precise meaning is not intended, the name surface_temperature
>> could be used, which strictly refers to the temperature at the interface.
>>
>> Best wishes
>>
>> Jonathan
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Received on Thu Jul 18 2013 - 15:31:38 BST
