Dear Charles
"Net downward" means downwelling minus upwelling. That clarification is put
in the definition of the standard name to make the user aware that they have
the choice between downwelling and net_downward. If the standard name just
said "downward" it wouldn't be clear which was intended. I don't think the
definition aims to exclude any mechanism. It means the flux which is incident
from above, whereas upwelling means the flux incident from below, and net
downward is the difference between them. At the surface, the net downward
flux is the part absorbed.
Cheers
Jonathan
----- Forwarded message from Charles Paxson <cpaxson at aer.com> -----
> Date: Mon, 6 May 2013 12:18:39 -0400
> From: Charles Paxson <cpaxson at aer.com>
> User-Agent: Thunderbird 2.0.0.24 (X11/20100311)
> To: CF-metadata at cgd.ucar.edu
> Subject: [CF-metadata] Shortwave Downward Radiation
>
> Dear cf-metadata community,
>
> We have two questions arising from considering whether the
> CF-Metadata /surface_downwelling_shortwave_flux_in_/air may be used
> as a standard name for the GOES-R product: /Downward Shortwave
> Radiation.
>
> /1) Does the "diffuse solar radiation incident on the surface"
> specifically include radiation that resulted from surface reflection
> then subsequent atmospheric scattering back down to the surface?
> This is not spelled out in the standard definition.
>
> 2) What does "net downward" mean, i.e. does it mean total downward
> radiation minus reflected radiation?
>
> The following is the background that lead us to our questions:
>
> The GOESR program will produce a product called "Downward Shortwave
> Radiation", and the CF Meta Data database maintains a standard name
> variable entitled "/surface_downwelling_shortwave_flux_in_/air".
> The GOESR definition and the CF Metadata definitions are similar,
> and the difference is in part that the CF Metadata definition
> includes the sentence: "It does not mean 'net downward'."
> Clarifying this sentence in the context of the GOESR definition will
> help us to decide whether to adopt this name as a standard name.
>
> The essential CF standard definition for
> /surface_downwelling_shortwave_flux_in_/air is: Surface downwelling
> shortwave is the sum of direct and diffuse solar radiation incident
> on the surface. It does not mean "net downward".
>
> The GOESR equivalent quantity is similar including both direct and
> diffuse radiation with the additional second order component:
> "/radiation that is reflected upward at the surface and subsequently
> reflected back to the surface by the atmosphere/".
>
> Our understanding is that the statement "It does not mean 'net
> downward'.", precludes the reflected component as well as secondary
> effects from the surface reflection.
>
> Sincerely,
>
> Charles
>
> --
> Charles Paxson
> System Engineer
> Atmospheric and Environmental Research (AER), Inc.
> a Verisk Analytics Company
> 131 Hartwell Avenue, Lexington, MA 02421-3126
> office: 781-761-2209
> fax:781-761-2299
> www.aer.com
>
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----- End forwarded message -----
Received on Mon May 06 2013 - 14:28:28 BST
