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)

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• 姓名標示 – 您必須指名出正確的製作者，和提供授權條款的連結，以及表示是否有對內容上做出變更。您可以用任何合理的方式來行動，但不得以任何方式表明授權條款是對您許可或是由您所使用。
• 相同方式分享 – 如果您利用本素材進行再混合、轉換或創作，您必須基於如同原先的相同或兼容的條款，來分布您的貢獻成品。

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您可以選擇您需要的授權條款。

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.