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.'
(See
http://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 "irradiance".'
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
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Received on Wed May 13 2015 - 03:59:46 BST
