Judith,
I wasn't trying to imply that radiance and irradiance were the same.
Just that one is in use, so I don't see a strong reason for the other to
be excluded. If you are good with what Jonathan has proposed, then I am
OK with them too. I was trying to champion an alternative viewpoint on
your behalf because I felt that some of your points were being missed.
Growing CF beyond it's climate model origins is a good thing, so I'm
glad you are helping to stretch it.
Grace and peace,
Jim
On 5/14/15 1:24 PM, Judith Lean wrote:
> Thanks Jim, these names are also excellent!
>
> Just a note - in our community radiance and irradiance are not the
> same - radiance typically refers to the radiative output from a finite
> area of the Sun?s disk (i..e, per steradian) whereas irradiance is the
> integral of radiance over the entire surface of the disk projected to
> the Earth.
> There may also be a subtle difference between radiative flux and
> irradiance in that some people take ?radiative flux? to refer to the
> flux density from the entire solar surface whereas irradiance refers
> just to the hemisphere projected (in our case) to earth?.but this is
> getting unnecessarily muddy.
>
> So why don?t you and Jonathan determine which names you prefer?and
> lets also wait to hear from Odele and Peter. I am guessing they will
> prefer the names with ?irradiance? (which is dear to our hearts) but I
> don?t mind ?radiative flux? (now that Jonathan has explained the
> history of its usage),
>
> Thanks to both you and Jonathan - its great that we are making progress!
> Namaste!
> Judith
>
>
>> On May 14, 2015, at 1:08 PM, Jim Biard <jbiard at cicsnc.org
>> <mailto:jbiard at cicsnc.org>> wrote:
>>
>> Hi.
>>
>> I've looked at definitions of terms and such in a few different
>> sources, and I'd like to suggest these standard names and
>> definitions. I'll explain reasons after.
>>
>> solar_irradiance_at_1au (W m-2) defined as:
>> "Solar" means originating from the Sun. 'Irradiance' means the flux
>> of radiant energy per unit area normal to the direction of flow of
>> radiant energy. '1au' means a distance of 1 Astronomical Unit (AU)
>> from the Sun. The solar irradiance at 1AU is the radiative flux per
>> unit area from the Sun normal to a vector with a length of 1 AU
>> integrated over all wavelengths.
>>
>> solar_irradiance_per_unit_wavelength_at_1au (W m-2 m-1) defined as:
>> "Solar" means originating from the Sun. 'Irradiance' means the flux
>> of radiant energy per unit area normal to the direction of flow of
>> radiant energy. 'Per_unit_wavelength' means '1au' means a distance of
>> 1 Astronomical Unit (AU) from the Sun. The solar irradiance per unit
>> wavelength at 1AU is the radiative flux per unit area from the Sun
>> normal to a vector with a length of 1 AU. A coordinate variable for
>> radiation wavelength should be given the standard name
>> radiation_wavelength and the bounds of this coordinate variable
>> should be used to specify the wavelength range(s) to which the data
>> values apply.
>>
>> Here's why I chose what I did.
>>
>> * I didn't use 'TOA' because this quantity could easily be measured
>> by a detector that is not in Earth orbit at all (for example, the
>> DSCOVR spacecraft could measure this quantity from the L1 point).
>> An Earth-centric term such as this appears to be inappropriate.
>> * I used 'solar' because this is radiant energy coming from the Sun.
>> * I didn't use 'shortwave' because, as Peter stated in a previous
>> email, their measurements include medium and long wavelengths.
>> Using this term implies a cutoff that isn't there. Use of
>> 'shortwave' as a euphemism for 'solar' is discipline-specific and
>> does not communicate well to other communities.
>> * I didn't use 'spectral' because it is a less precise term than
>> 'per_unit_wavelength', and this is quite consistent with the
>> existing body of standard names. Particularly, a measurement
>> taken per unit wavelength and one taken per unit frequency have
>> different values and different units, yet both could be
>> considered to be spectral measurements.
>> * I used 'irradiance' because we have quite a few terms that use
>> 'radiance'. I don't find any imprecision couched in these terms,
>> and both are in wide scientific use, so why should we shy away
>> from them? I particularly don't see any reason why we should use
>> 'radiance' and not 'irradiance'.
>> * I used 'at_1au' because this normalizing distance is a key part
>> of the measurements, and it doesn't carry the same level of
>> Earth-centric implication as using an orbit description does. The
>> sphere at 1 AU from the Sun is the surface at which this
>> measurement applies. The measurement could also be taken for a
>> sun in a different solar system that had no planet at that distance.
>>
>> It's true that the standard names aren't primarily intended as search
>> terms. They are more intended for precise definitions of quantities
>> and how they fit into the 'taxonomy of quantities'. At the same time,
>> I think we need to be open to allowing valid, non-Earth-centric
>> standard names. We also need to be careful that we don't make the
>> names unnecessarily obscure.
>>
>> Grace and peace,
>>
>> Jim
>>
>> On 5/13/15 8:58 AM, Peter Pilewskie wrote:
>>> On 5/13/2015 6:45 AM, Jim Biard wrote:
>>>> Hi.
>>>>
>>>> You guys have done a lot of good work, and I don't want to slow
>>>> things down, but I would appreciate it if one of the proposers
>>>> could explain why the distance from the Sun is significant to this
>>>> standard name,
>>> Most users of the data prefer that solar irradiance is referenced to
>>> the standard distance of 1 AU rather than have orbital variations
>>> in the data. In the rare case where someone wants solar irradiance
>>> on a specific day, it is simple to adjust by the inverse of distance
>>> squared. We know this from many years serving the community this
>>> data. This includes climate modelers, radiative transfer
>>> specialists, users interested in calculating reaction rates,
>>> renewable energy specialists, and many others. Users of the data
>>> must know whether the data has been "detrended" for orbital
>>> variability. It is about 6%, more than an order of magnitude larger
>>> than solar cycle variability.
>>>
>>>
>>>> and whether or not the word 'shortwave' is appropriate for the data
>>>> quantity they are describing.
>>>
>>> I covered this in the previous message: "shortwave" covers only part
>>> of the spectral range. TSI covers all wavelengths. 'Shortwave' is
>>> inappropriate.
>>>
>>>
>>> Peter
>>>
>>>
>>>
>>>>
>>>> Grace and peace,
>>>>
>>>> Jim
>>>>
>>>> On 5/13/15 5:59 AM, alison.pamment at stfc.ac.uk wrote:
>>>>> Dear Odele, Judith, Peter et al,
>>>>>
>>>>> Thank you for your two proposals which have now been added to the list of CF standard names under discussion:http://cfeditor.ceda.ac.uk/proposals/1?status=active&namefilter=&proposerfilter=Odele&descfilter=&unitfilter=&yearfilter=&filter+and+display=Filter.
>>>>>
>>>>> TSI:
>>>>> You proposed toa_total_solar_irradiance (Wm-2) defined as:
>>>>> ' The solar power per unit area integrated over all wavelengths that is incident at the top of the Earth's atmosphere (TOA), at a standard distance of one Astronomical Unit (1 AU) from the Sun, in units of Watts per square meter.'
>>>>>
>>>>> I agree with John Graybeal's comment that the units should not form part of the standard name definition, but rather should be listed as "canonical units" in the standard name table. This is standard practice within CF.
>>>>>
>>>>> Jonathan Gregory has pointed out that we do have the existing standard name toa_incoming_shortwave_flux (W m-2) defined as:
>>>>> ' "shortwave" means shortwave radiation. "toa" means top of atmosphere. The TOA incoming shortwave flux is the radiative flux from the sun i.e. the "downwelling" TOA shortwave flux. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.'
>>>>>
>>>>> The definition of the existing name does not mention a standardized distance of 1AU between Earth and sun, and if this consideration is important then I think you probably do need a separate name for what is essentially a theoretical quantity.
>>>>>
>>>>> In climate modelling the term "shortwave" is commonly used to mean solar radiation and indeed this is the convention used in many existing CF standard names. (It is probably worth adding a sentence to the definition of all shortwave names to make that point clear). I agree with Jonathan that there is no need to use the word "total" in the name itself because the quantity would be assumed to represent all "shortwave" wavelengths unless otherwise specified. I also agree with Jonathan regarding the use of "irradiance" as a term. Many existing longwave and shortwave standard names contain the following text in their definition: 'When thought of as being incident on a surface, a radiative flux is sometimes called "irradiance",' but the term "irradiance" does not actually appear in the names themselves.
>>>>>
>>>>> Taking all these points into consideration, I suggest the following standard name:
>>>>>
>>>>> toa_incoming_shortwave_flux_assuming_circular_orbit (Wm-2) defined as:
>>>>> ' "shortwave" means shortwave radiation. "toa" means top of atmosphere. The quantity with standard name toa_incoming_shortwave_flux_assuming_circular_orbit is the radiative flux from the sun, i.e. the downwelling TOA shortwave flux assuming that the earth is in a circular orbit around the sun with radius 1 AU. A phrase assuming_condition indicates that the named quantity is the value which would obtain if all aspects of the system were unaltered except for the assumption of the circumstances specified by the condition. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. When thought of as being incident on a surface, a radiative flux is sometimes called "irradiance".'
>>>>>
>>>>> I appreciate that the name itself looks rather different from the original proposal, but I think it is consistent with existing standard names and clearly distinct from the quantity that does not specify earth-sun distance. I'd welcome comments on this idea.
>>>>>
>>>>> SSI:
>>>>>
>>>>> You proposed toa_solar_spectral_irradiance (W m-2 m-1) defined as:
>>>>> 'The solar power per unit area per unit wavelength that is incident at the top of the Earth's atmosphere, at a standard distance of one Astronomical Unit (1 AU) from the Sun, in units of Watts per square meter per nanometer (1 nm = 10 ^-9 m).'
>>>>>
>>>>> Again the canonical units should be separated out from the definition and they should indeed be W m-2 m-1 in the standard name table. This would still allow you to use W m-2 nm-1 in your data files because the UDunits software which CF specifies for unit conversion would be able to convert easily between the two.
>>>>>
>>>>> As Jonathan pointed out, we no longer use the word "spectral" in standard names but rather "per_unit_wavelength" or "per_unit_wavenumber". (We could also add "per_unit_frequency" if it is ever needed).
>>>>>
>>>>> We do have another proposal for a similar standard name:
>>>>> toa_solar_irradiance_per_unit_wavelength (W m-2 m-1), currently defined as:
>>>>> ' "toa" means top of atmosphere. "solar" indicates contributions from the sun. Irradiance is the radiant power per unit area incident at a surface.'
>>>>> (Seehttp://cfeditor.ceda.ac.uk/proposals/1?status=active&namefilter=solar&proposerfilter=Randy&descfilter=&unitfilter=&yearfilter=&filter+and+display=Filter)
>>>>> but again this proposal makes no mention of a 1AU orbital radius, so I am not sure that it is really the same quantity that you require.
>>>>>
>>>>> Taking these points into account and again replacing "solar" with "shortwave" we arrive at:
>>>>>
>>>>> toa_incoming_shortwave_flux_per_unit_wavelength_assuming_circular_orbit (W m-2 m-1) defined as:
>>>>> '"shortwave" means shortwave radiation. "toa" means top of atmosphere. The quantity with standard name toa_incoming_shortwave_flux_per_unit_wavelength_assuming_circular_orbit is the radiative flux from the sun, i.e. the downwelling TOA shortwave flux assuming that the earth is in a circular orbit around the sun with radius 1 AU. A coordinate variable for radiation wavelength should be given the standard name radiation_wavelength and the bounds of this coordinate variable should be used to specify the wavelength range(s) to which the data values apply. A phrase assuming_condition indicates that the named quantity is the value which would obtain if all aspects of the system were unaltered except for the assumption of the circumstances specified by the condition. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. When thought of as being incident on a surface, a radiative flux is sometimes called "irradian
>>>>> ce".'
>>>>>
>>>>> Again, comments are welcome.
>>>>>
>>>>> Best wishes,
>>>>> Alison
>>>>>
>>>>> ------
>>>>> Alison Pamment Tel: +44 1235 778065
>>>>> NCAS/Centre for Environmental Data Archival Email:alison.pamment at stfc.ac.uk
>>>>> STFC Rutherford Appleton Laboratory
>>>>> R25, 2.22
>>>>> Harwell Oxford, Didcot, OX11 0QX, U.K.
>>>>>
>>>>>
>>>>>
>>>>>> -----Original Message-----
>>>>>> From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf
>>>>>> Of Jonathan Gregory
>>>>>> Sent: 06 May 2015 18:27
>>>>>> To:cf-metadata at cgd.ucar.edu
>>>>>> Cc: Odele Coddington;judith.lean at nrl.navy.mil; Peter Pilewskie
>>>>>> Subject: Re: [CF-metadata] New standard name requests for TSI and SSI
>>>>>>
>>>>>> Dear Odele et al.
>>>>>>
>>>>>> Thanks for your proposals.
>>>>>>
>>>>>> I'm not sure whether by TOA irradiance you mean the flux incident normal
>>>>>> to
>>>>>> the Earth's surface or parallel to the vector between Sun and Earth. If it is
>>>>>> the former, we already have a standard name for it viz
>>>>>> toa_incoming_shortwave_flux
>>>>>> If it is the latter, does it need "TOA"? In that case it's a quantity in
>>>>>> space, not really do with the Earth itself, just at the right distance.
>>>>>>
>>>>>> We don't so far use the word irradiance in standard names (except in the
>>>>>> phrase spherical_irradiance).
>>>>>>
>>>>>> I think that "total" should be omitted. It is the usual convention in
>>>>>> standard names that if there is no qualifier the quantity should be
>>>>>> understood
>>>>>> as inclusive. It could be restricted to a range of wavelengths by giving it
>>>>>> a coordinate variable for wavelength.
>>>>>>
>>>>>> Finally, we don't use the word "spectral" in standard names. It was replaced
>>>>>> with per_unit_wavelength to be more explicit e.g.
>>>>>> surface_downwelling_radiative_flux_per_unit_wavelength_in_air
>>>>>>
>>>>>> Cheers
>>>>>>
>>>>>> Jonathan
>>>>>>
>>>>>>> We are proposing two new standard names for Total Solar Irradiance (TSI)
>>>>>>> and Solar Spectral Irradiance (SSI) at the top of the atmosphere. Your
>>>>>>> comments on these two proposals would be appreciated.
>>>>>>>
>>>>>>> Regards,
>>>>>>> Odele Coddington and Peter Pilewskie (CU-Boulder/LASP) and Judith Lean
>>>>>> (NRL)
>>>>>>> standard name:
>>>>>>> toa_total_solar_irradiance
>>>>>>>
>>>>>>> definition:
>>>>>>> The solar power per unit area integrated over all wavelengths that is
>>>>>>> incident at the top of the Earth???s atmosphere (TOA), at a standard
>>>>>> distance
>>>>>>> of one Astronomical Unit (1 AU) from the Sun, in units of Watts per square
>>>>>>> meter.
>>>>>>>
>>>>>>> canonical units:
>>>>>>> W m-2
>>>>>>>
>>>>>>> standard name:
>>>>>>> toa_solar_spectral_irradiance
>>>>>>>
>>>>>>> definition:
>>>>>>> The solar power per unit area per unit wavelength that is incident at the
>>>>>>> top of the Earth???s atmosphere, at a standard distance of one
>>>>>> Astronomical
>>>>>>> Unit (1 AU) from the Sun, in units of Watts per square meter per
>>>>>> nanometer
>>>>>>> (1 nm = 10 ^???9 m).
>>>>>>>
>>>>>>> canonical units:
>>>>>>> W m-2 m-1
>>>>>> _______________________________________________
>>>>>> 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
>>>>
>>>> --
>>>> <Mail Attachment.png> <http://www.cicsnc.org/> Visit us on
>>>> Facebook <http://www.facebook.com/cicsnc> *Jim Biard*
>>>> *Research Scholar*
>>>> Cooperative Institute for Climate and Satellites NC
>>>> <http://cicsnc.org/>
>>>> North Carolina State University <http://ncsu.edu/>
>>>> NOAA National Centers for Environmental Information
>>>> <http://ncdc.noaa.gov/>
>>>> /formerly NOAA?s National Climatic Data Center/
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>>>>
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>>>
>>>
>>> --
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>>> University of Colorado
>>> Laboratory for Atmospheric and Space Physics
>>> Department of Atmospheric and Oceanic Sciences
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>>> Boulder, CO 80303-7819
>>> 303 735 5589
>>> peter.pilewskie at lasp.colorado.edu
>>>
>>
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>
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/formerly NOAA?s National Climatic Data Center/
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