Diffuse sky radiation

Diffuse sky radiation is <a href="/facts/Solar_radiation/SI26I7aD">solar radiation</a> reaching the <a href="/facts/Earth/HLLmDfj0">Earth</a>'s surface after having been <a href="/facts/Scattering/nMou7lEH">scattered</a> from the direct solar beam by <a href="/facts/Molecule/N9ljSfFq">molecules</a> or <a href="/facts/Particulates/RleGr5E6">particulates</a> in the <a href="/facts/Earth%27s_atmosphere/FV97Am25">atmosphere</a>. It is also called sky radiation, the determinative process for changing the colors of the <a href="/facts/Sky/wwvQ84J1">sky</a>. Approximately 23% of direct incident radiation of total <a href="/facts/Sunlight/WPkJRC7s">sunlight</a> 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 <a href="/facts/Photon_diffusion/eQav2ADE">photon diffused</a> skylight radiation.
The dominant radiative scattering processes in the atmosphere are <a href="/facts/Rayleigh_scattering/o0MQtPMM">Rayleigh scattering</a> and <a href="/facts/Mie_scattering/5mJc3SrT">Mie scattering</a>; they are <a href="/facts/Elastic_scattering/51u9WlE1">elastic</a>, 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: 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).

Diffuse sky radiation open-in-new

Diffuse sky radiation