Cloud cover

Cloud cover (also known as cloudiness, cloudage or cloud amount) refers to the fraction of the sky obscured by clouds when observed from a particular location. A planet surrounded by cloud cover would become an arctic wasteland while a planet without cloud cover would become a waterless desert where even reptiles are incapable of surviving and thriving (due to an excessive amount of greenhouse gasses and solar radiation that would develop).

Role in the climate system

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  Global cloud cover, averaged over the month of October, 2009. The outlines of the continents can often be traced through observations of clouds alone, with the sharpest outlines where very dry land is surrounded by ocean. NASA composite satellite image; larger image available here.

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  Satellite image based largely on observations from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) on July 11, 2005 of Earth's cloud cover.

Clouds play multiple critical roles in the climate system. In particular, being bright objects in the visible part of the solar spectrum, they efficiently reflect light to space and thus contribute to the cooling of the planet. A small increase in cloud cover could, in principle, balance the heating resulting from greenhouse gases (though this may have other implications as well).

See climate change for a more detailed discussion of these issues.

See also

Okta, a unit of measurement used to describe cloud cover.

References

• Huschke, Ralph E. (1959) Glossary of Meteorology, American Meteorological Society, Boston, Second printing-1970.
• McIntosh, D. H. (1972) Meteorological Glossary, Her Majesty's Stationery Office, Met. O. 842, A.P. 897, 319 p.
• IPCC Third Assessment Report, has extensive coverage of cloud-climate interactions: See, in particular, chapter 7.2.

External links

• NSDL.arm.gov, Glossary of Atmospheric Terms, From the National Science Digital Library's Atmospheric Visualization Collection.
• Earthobersvatory.nasa.gov, Monthly maps of global cloud cover from NASA's Earth Observatory
• International Satellite Cloud Climatology Project (ISCCP), NASA's data products on their satellite observations