Editing Diffuse sky radiation (section)

{{Short description|Solar radiation reaching the Earth's surface}}
{{Redirect|Red sky||Red Sky (disambiguation)}}
{{Use mdy dates|date=November 2024}}
{{Use American English|date=September 2020}}
[[File:Rayleigh sunlight scattering.png|thumb|upright=1.9|In [[Earth's atmosphere]], the dominant scattering efficiency of [[sky blue|blue light]] is compared to [[Visible spectrum#Spectral colors|red or green]] light. Scattering and absorption are major causes of the [[attenuation]] of sunlight radiation by the atmosphere. During broad [[daylight]], the sky is blue due to [[Rayleigh scattering]], while around sunrise or sunset, and especially during [[twilight]], [[Chappuis absorption|absorption]] of irradiation by [[Ozone#Spectroscopic properties|ozone]] helps maintain blue color in the evening sky. At sunrise or sunset, tangentially incident solar rays illuminate clouds with orange to red hues.]]
[[File:Spectrum of blue sky.svg|thumb|upright=1.9|The visible spectrum, approximately 380 to 740 nanometers (nm),<ref>{{cite book | title = Biology: Concepts and Applications | author = Starr, Cecie | publisher = Thomson Brooks/Cole | year = 2006| isbn = 978-0-534-46226-0 | url = https://archive.org/details/biologyconceptsa06edstar| url-access = registration | page = [https://archive.org/details/biologyconceptsa06edstar/page/94 94] }}</ref> shows the atmospheric water absorption band and the solar [[Fraunhofer lines]]. The blue sky spectrum contains light at all visible wavelengths with a broad maximum around 450–485 nm, the wavelengths of the color blue.]]

'''Diffuse sky radiation''' is [[solar radiation]] reaching the [[Earth]]'s surface after having been [[scattering|scattered]] from the direct solar beam by [[molecule]]s or [[particulates]] in the [[Earth's atmosphere|atmosphere]]. It is also called '''sky radiation''',  the determinative process for changing the colors of the [[sky]]. Approximately 23% of direct incident radiation of total [[sunlight]] is removed from the direct solar beam by scattering into the atmosphere; of this amount (of incident radiation)  about two-thirds ultimately reaches the earth as [[photon diffusion|photon diffused]] skylight radiation.{{citation needed|date=March 2016}}

The dominant radiative scattering processes in the atmosphere are [[Rayleigh scattering]] and [[Mie scattering]]; they are [[elastic scattering|elastic]], meaning that a photon of light can be deviated from its path without being absorbed and without changing wavelength.

Under an overcast sky, there is no direct sunlight, and all light results from diffused skylight radiation.

Proceeding from analyses of the aftermath of the eruption of the Philippines volcano Mount Pinatubo (in June 1991) and other studies:<ref name="web.archive.org"/><ref>{{cite journal |last1=Young |first1=Donald |last2=Smith |first2=William |title=Effect of Cloudcover on Photosynthesis and Transpiration in the Subalpine Understory Species Arnica Latifolia |journal=Ecology |pages=681–687 |doi=10.2307/1937189 |date=1983|volume=64 |issue=4 |jstor=1937189 |bibcode=1983Ecol...64..681Y }}</ref>  Diffused skylight, owing to its intrinsic structure and behavior, can illuminate under-canopy leaves, permitting more efficient total whole-plant photosynthesis than would otherwise be the case; this in stark contrast to the effect of totally clear skies with direct sunlight that casts shadows onto understory leaves and thereby limits plant photosynthesis to the top canopy layer, [[#The diffused skylight effect|(see below)]].