Add missing surface upwelling radiative flux in the longwave for use in CMIP7

[fmoconnor]

Following on from the discussion in #58, we identified a missing CF name in the diagnosis of surface upwelling longwave radiative fluxes, from a diagnostic call to a model's radiation scheme under clear-sky and "clean", i.e., no aerosol conditions.

From that discussion, LW emission from the surface is based on temperature and thus the same for all-sky vs clear-sky since the clear-sky calculation is not actually interactively changing surface temperature. However, when models treat surface emissivity less than 1, some of the downwelling LW from the lower atmosphere to the surface is not perfectly absorbed and instead will be reflected (i.e., <1 emissivity implies >0 reflectivity). This reflection is then included as part of the longwave upwelling diagnosis and the amount reflected is dependent on the amount of downwelling, which in turn is dependent on if/where there is a cloud above.

It means that the all-sky vs clear-sky radiation calculation would be impacted. It also means that in the case of any atmospheric constituent that absorbs and/or scatters in the longwave, there will be differences in radiative flux diagnostics from any corresponding double radiation call between all-sky and clear-sky conditions. Therefore, there is a requirement for a corresponding CF name for the surface upwelling radiative flux from a diagnostic radiation call assuming clear-sky conditions and "no aerosol" (i.e., surface_upwelling_longwave_flux_in_air_assuming_clear_sky_and_no_aerosol).

Therefore, this issue has been opened in order to propose this new addition to the CF standard.

Proposer's name Fiona O'Connor

Date 12 November 2024

- Term surface_upwelling_longwave_flux_in_air_assuming_clear_sky_and_no_aerosol

- Description The surface called "surface" means the lower boundary of the atmosphere. The term "longwave" means longwave radiation. Upwelling radiation is radiation from below. It does not mean "net upward". The sign convention is that "upwelling" is positive upwards and "downwelling" is positive downwards. When thought of as being incident on a surface, a radiative flux is sometimes called "irradiance". In addition, it is identical with the quantity measured by a cosine-collector light-meter and sometimes called "vector irradiance". In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. 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. "Clear sky" means in the absence of clouds.

- Units W/m2

[github-actions]

Thank you for your proposal. These terms will be added to the cfeditor (http://cfeditor.ceda.ac.uk/proposals/1) shortly. Your proposal will then be reviewed and commented on by the community and Standard Names moderator.