Caption

Why the polar regions are colder: Effect of the Earth's shape and atmosphere on incoming solar radiation.

Compared to equatorial regions (b), incoming solar radiation of the polar regions (a) is less intense for two reasons:

1. the solar radiation arrives at an oblique angle nearer the poles, so that the energy spreads over a larger surface area, lessening its intensity.
2. The radiation travels a longer distance through the atmosphere, which absorbs, scatters and reflects the solar radiation.

Tropical areas (i.e. lower latitudes, nearer the equator) receive solar radiation which is closer to vertical.

The angle of incidence of the rays, combined with the albedo of the surface has also a strong influence on the amount of energy being absorbed (or reflected) at the surface. In the ice-covered polar zones, almost all direct energy from the sun is reflected because it is white and the angle is small. In short, the angle of incidence affects the heating of the surface in 3 different ways: length of atmospheric track, variable flux and variable reflection

For simplicity, the diagram ignores the axial tilt of the Earth, which causes each pole to slip into darkness for around 6 months of the year, and means the equator's ground is generally not perpendicular with the sun's light.

About

• Created in Inkscape (v0.45)

Based on diagrams in:

• Ecology: Theories and Applications, 4th Edition, Peter Stiling. Figure 14.2. page 231.
• Biology, third edition. Arms & Camp. Figure 49-1. page 973.
• ...and from feedback at en:Wikipedia:Picture_peer_review/Oblique_rays

Other versions

• 
  Original
• 
  With land mass
• 
  Northern Winter axial tilt
• File:Oblique rays 04 Penga
• Slight Spring or Autumn tilt (my preferred version)
  Slight Spring or Autumn tilt (my preferred version)

See also

• Image:Flux surface.jpg, related diagram (Portuguese)

Licensing

Diagram credit: Peter Halasz. (User:Pengo)

Moi, en tant que détenteur des droits d’auteur sur cette œuvre, je la publie sous les licences suivantes :

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Ɣuṛ-k tilelli:

• i beṭṭu – akken ad tneɣleḍ, ad tzuzreḍ neɣ ad tebḍuḍ amahil-agi
• i uṣeggem – i uṣeggem n umahil

Ddaw n tiwtilin-agi:

• bab – Yessefk ad d-bedreḍ isem n umeskar aneṣli s wudem yettwammlen sɣuṛ ameskar n umahil neɣ bab n izerfan i k-imudden tasiregt (mačči s wudem yemmalen am akken yettmuddu-yak afus neɣ yeqbel aseqdec-it n umahil).
• bḍut akken yella – Ma tbeddleḍ, teskelteḍ, neɣ tebniḍ ɣef umahil-agi, yessefk ad tezzuzreḍ amahil i d-yeffɣen ɣas ddaw n turagt-nni neɣ turagt icuban ɣuṛ-s.

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Tzemreḍ ad ferneḍ yiwet seg turagin-agi.

For the Creative Commons license, please give attribution to:

• Peter Halasz
• and/or, link to this image page: http://commons.wikimedia.org/wiki/File:Oblique_rays_02_Pengo.svg

Although not a requirement of the license, if you use this image in print or media other than the web, I would appreciate it if you let me know. Please contact me if you require alternate licensing.