Diffuse sky radiation

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"Red sky" redirects here. For other uses, see Red Sky (disambiguation).

Earth's atmosphere, the dominant scattering efficiency of blue light is compared to 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, absorption of irradiation by ozone
helps maintain blue color in the evening sky. At sunrise or sunset, tangentially incident solar rays illuminate clouds with orange to red hues.
The visible spectrum, approximately 380 to 740 nanometers (nm),[1] 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

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 diffused skylight radiation.[citation needed
]

The dominant radiative scattering processes in the atmosphere are Rayleigh scattering and Mie scattering; they are 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:[2][3] 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, (see below).

Color

A clear daytime sky, looking toward the zenith

unsaturated blue light.[5] The explanation of blue color by Rayleigh in 1871 is a famous example of applying dimensional analysis to solving problems in physics;[6]
.

Scattering and absorption are major causes of the

geometric optics
begin to apply at higher ratios.

Daily at any global venue experiencing sunrise or sunset, most of the solar beam of visible sunlight arrives nearly tangentially to Earth's surface. Here, the path of sunlight through the atmosphere is elongated such that much of the blue or green light is scattered away from the line of perceivable visible light. This phenomenon leaves the Sun's rays, and the clouds they illuminate, abundantly orange-to-red in colors, which one sees when looking at a sunset or sunrise.

For the example of the Sun at

diatomic gases N
2 and O
2. Near sunset and especially during twilight, absorption by ozone (O
3) significantly contributes to maintaining blue color
in the evening sky.

Under an overcast sky

There is essentially no direct sunlight under an overcast sky, so all light is then diffuse sky radiation. The flux of light is not very wavelength-dependent because the cloud droplets are larger than the light's wavelength and scatter all colors approximately equally. The light passes through the translucent clouds in a manner similar to frosted glass. The intensity ranges (roughly) from 1⁄6 of direct sunlight for relatively thin clouds down to 1⁄1000 of direct sunlight under the extreme of thickest storm clouds.[citation needed]

As a part of total radiation

One of the equations for total solar radiation is:[7]

where Hb is the beam radiation irradiance, Rb is the tilt factor for beam radiation, Hd is the diffuse radiation irradiance, Rd is the tilt factor for diffuse radiation and Rr is the tilt factor for reflected radiation.

Rb is given by:

where δ is the

solar declination, Φ is the latitude, β is an angle from the horizontal and h is the solar hour angle
.

Rd is given by:

and Rr by:

where ρ is the

reflectivity
of the surface.

Agriculture and the eruption of Mt. Pinatubo

A Space Shuttle (Mission STS-43) photograph of the Earth over South America taken on August 8, 1991, which captures the double layer of Pinatubo aerosol clouds (dark streaks) above lower cloud tops.

The eruption of the

net primary production,[21] of global plant life, resulting in the increase of the carbon sink effect of global photosynthesis.[2][14] The mechanism by which the increase in plant growth was possible, was that the 30% reduction of direct sunlight can also be expressed as an increase or "enhancement" in the amount of diffuse sunlight.[2][18][22][14]

The diffused skylight effect

soft sunlight
conditions, that permits photosynthesis on leaves under the canopy.

This diffused skylight, owing to its intrinsic nature, can illuminate under-

understorey leaves, limiting plant photosynthesis to the top canopy layer.[2][14] This increase in global agriculture from the volcanic haze layer also naturally results as a product of other aerosols that are not emitted by volcanoes, such, "moderately thick smoke loading" pollution, as the same mechanism, the "aerosol direct radiative effect" is behind both.[16][24][25]

See also

References

  1. ISBN 978-0-534-46226-0
    .
  2. ^ a b c d e f g "Large Volcanic Eruptions Help Plants Absorb More Carbon Dioxide From the Atmosphere : News". March 16, 2010. Archived from the original on March 16, 2010. Retrieved April 4, 2018.
  3. JSTOR 1937189
    .
  4. ^ "Rayleigh scattering." Encyclopædia Britannica. 2007. Encyclopædia Britannica Online. retrieved November 16, 2007.
  5. doi:10.1119/1.1858479
    .
  6. ^ "Craig F. Bohren, "Atmospheric Optics", Wiley-VCH Verlag GmbH, page 56" (PDF). wiley-vch.de. Retrieved April 4, 2018.
  7. ISBN 978-81-224-1540-7
    .
  8. ISBN 978-0-792-32278-8
    .
  9. ^ "Mt. Pinatubo's cloud shades global climate". Science News. Retrieved March 7, 2010.
  10. ^ Program, Volcano Hazards. "Hawaiian Volcano Observatory". hvo.wr.usgs.gov. Retrieved April 4, 2018.
  11. ^ "Mercado". pubs.usgs.gov. Retrieved April 4, 2018.
  12. ^ "Mt. pinatubo (LK): Biosphere - ESS". sites.google.com. Retrieved April 4, 2018.
  13. ^ "Cooling Following Large Volcanic Eruptions Corrected for the Effect of Diffuse Radiation on Tree Rings. Alan Robock, 2005. See Figure 1 for a graphic of the recorded change in solar iiradiation" (PDF). rutgers.edu. Retrieved April 4, 2018.
  14. ^ a b c d e f LARGE VOLCANIC ERUPTIONS HELP PLANTS ABSORB MORE CARBON DIOXIDE FROM THE ATMOSPHERE
  15. S2CID 28228518
    .
  16. ^ a b Evaluating aerosol direct radiative effects on global terrestrial ecosystem carbon dynamics from 2003 to 2010. Chen et al., Tellus B 2014; 66, 21808, Published by the international meteorological institute in Stockholm.
  17. ^ "Cooling Following Large Volcanic Eruptions Corrected for the Effect of Diffuse Radiation on Tree Rings. Alan Robock, 2005. See Figure 2 for a record of this" (PDF). rutgers.edu. Retrieved April 4, 2018.
  18. ^
    Bibcode:2001AGUFM.B51A0194G
    .
  19. ^ "Response of a Deciduous Forest to the Mount Pinatubo Eruption: Enhanced Photosynthesis. Gu et al., 28 March 2003 Journal of Science Vol 299" (PDF). utoledo.edu. Archived from the original (PDF) on March 4, 2016. Retrieved April 4, 2018.
  20. ^ "CO2 Science". www.co2science.org. Retrieved April 4, 2018.
  21. ^ http://earthobservatory.nasa.gov/Features/GlobalGarden/ Global Garden gets greener. NASA 2003
  22. ^ "Cooling Following LargeVolcanic Eruptions Corrected for the Effect of Diffuse Radiation on Tree Rings. Alan Robock, 2005. Figure 1" (PDF). rutgers.edu. Retrieved April 4, 2018.
  23. S2CID 236541532
    .
  24. doi:10.1029/2001GB001441
  25. doi:10.1029/2004GL020915

Further reading

External links
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