Hello again,
What we map to the 'solar_irradiance' Standard name are parameters such as 'Downwelling vector irradiance as energy of electromagnetic radiation (solar wavelengths) in the atmosphere by pyranometer'. So in the use case I was thinking of it's both a horizontal surface and a surface perpendicular to the direction of flow of the radiant energy i.e. we have made an assumption the the direction of flow of the radiant energy is perpendicular to the Earth's surface.
Consequently, I would amend the definition as below rather than redefining from scratch with the risk you pointed out of changing the semantics of existing data sets.
"Irradiance" means the power per unit area (called radiative flux in other standard names), the area being normal to the direction of flow of the radiant energy. The area is a horizontal surface for radiant energy flowing perpendicular to the Earth's surface.
Cheers, Roy.
Please note that I partially retired on 01/11/2015. I am now only working 7.5 hours a week and can only guarantee e-mail response on Wednesdays, my day in the office. All vocabulary queries should be sent to enquiries at bodc.ac.uk. Please also use this e-mail if your requirement is urgent.
________________________________
From: martin.juckes at stfc.ac.uk <martin.juckes at stfc.ac.uk>
Sent: 26 January 2018 16:52
To: Lowry, Roy K.; cf-metadata at cgd.ucar.edu
Subject: RE: Definiton of solar_irradiance
Dear Roy,
If we were starting from scratch I would recommend the following:
Solar irradiance is the power per unit area of the solar radiation received from above at horizontal surface. It is distinct from the Direct Normal Irradiance (which refers to radiation received by a surface perpendicular to rays travelling from the sun) and the Total Solar Irradiance (which is the mean value of Direct Normal Irradiance at a standard distance from the sun).
I am, however, concerned that people may have already, on the basis of the current definition, used the term for Total Solar Irradiance.
regards,
Martin
________________________________________
From: Lowry, Roy K. [rkl at bodc.ac.uk]
Sent: 26 January 2018 16:03
To: Juckes, Martin (STFC,RAL,RALSP); cf-metadata at cgd.ucar.edu
Subject: Re: Definiton of solar_irradiance
Dear Martin,
I agree that the current definition reflects more an astrophysics textbook rather than common usage of the Standard Name and so I would support tweaking the wording as you suggest. Care to come up with the replacement wording to be used?
Cheers, Roy.
Please note that I partially retired on 01/11/2015. I am now only working 7.5 hours a week and can only guarantee e-mail response on Wednesdays, my day in the office. All vocabulary queries should be sent to enquiries at bodc.ac.uk. Please also use this e-mail if your requirement is urgent.
________________________________
From: martin.juckes at stfc.ac.uk <martin.juckes at stfc.ac.uk>
Sent: 26 January 2018 15:57
To: Lowry, Roy K.; cf-metadata at cgd.ucar.edu
Subject: RE: Definiton of solar_irradiance
Hello Roy,
I suspected that there might be such a usage ... but don't you agree that the current CF definition, which I've quoted below, is inconsistent with this? But it could be adapted with a small change of wording,
regards,
Martin
________________________________
From: Lowry, Roy K. [rkl at bodc.ac.uk]
Sent: 26 January 2018 15:51
To: Juckes, Martin (STFC,RAL,RALSP); cf-metadata at cgd.ucar.edu
Subject: Re: Definiton of solar_irradiance
Hello Martin,
>From an oceanographic perspective I had always thought of solar (and other waveband) irradiance as the energy incident on the sea surface, which is a horizontal surface. So, I would like to think of solar_irradiance as being horizontal_solar_irradiance and if any new Standard Name is required to cover the current Vaisala instrumentation use case then that should be normal_standard_irradiance.
Cheers, Roy.
Please note that I partially retired on 01/11/2015. I am now only working 7.5 hours a week and can only guarantee e-mail response on Wednesdays, my day in the office. All vocabulary queries should be sent to enquiries at bodc.ac.uk. Please also use this e-mail if your requirement is urgent.
________________________________
From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> on behalf of martin.juckes at stfc.ac.uk <martin.juckes at stfc.ac.uk>
Sent: 26 January 2018 13:37
To: cf-metadata at cgd.ucar.edu
Subject: [CF-metadata] Definiton of solar_irradiance
Hello,
the cf standard name has a definition:
The quantity with standard name solar_irradiance, often called Total Solar Irradiance (TSI), is the radiation from the sun integrated over the whole electromagnetic spectrum and over the entire solar disk. The quantity applies outside the atmosphere, by default at a distance of one astronomical unit from the sun, but a coordinate or scalar coordinate variable of distance_from_sun can be used to specify a value other than the default. "Irradiance" means the power per unit area (called radiative flux in other standard names), the area being normal to the direction of flow of the radiant energy.
My question is about the last phrase, which I have highlighted. The flow of radiant energy from the sun at the top of the atmosphere is directed away from the sun .. so this definition would imply that the irradiance is defined relative to a fixed plane in the solar coordinate system. This is OK for solar physicists, but atmospheric scientists are sometime interested in irradiance relative to a horizontal surface.
Vaisalla distinguish between the two by defining "horizontal solar irradiance" to be the irradiance on a horizontal surface and "normal solar irradiance" to be irradiance on a surface perpendicular to a line to the sun (<UrlBlockedError.aspx>
http://www.3tier.com/en/support/solar-online-tools/what-solar-values-are-shown-map/ ).
Should "solar_irradiance" apply to both usages, or do we need a new standard name, e.g. "horizonatl_solar_irradiance"?
regards,
Martin
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