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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本文件采用知识共享署名-相同方式共享 3.0 未本地化版本许可协议授权。

您可以自由地：

• 共享 – 复制、发行并传播本作品
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惟须遵守下列条件：

• 署名 – 您必须对作品进行署名，提供授权条款的链接，并说明是否对原始内容进行了更改。您可以用任何合理的方式来署名，但不得以任何方式表明许可人认可您或您的使用。
• 相同方式共享 – 如果您再混合、转换或者基于本作品进行创作，您必须以与原先许可协议相同或相兼容的许可协议分发您贡献的作品。

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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.