Cloud cover

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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.

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.[1] Okta is the usual unit of measurement of the cloud cover.

Role in the climate system[edit]

Partial cloud cover over the North Atlantic Ocean.
Global cloud cover, averaged over the month of October, 2009. The image shows that 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.
These maps display the fraction of Earth's area that was cloudy on average during each month from January 2005 to August 2013. The measurements were collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite. Colors range from blue (no clouds) to white (totally cloudy). Like a digital camera, MODIS collects information in gridded boxes, or pixels. Cloud fraction is the portion of each pixel that is covered by clouds. Colors range from blue (no clouds) to white (totally cloudy).[2] (click for more detail)

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. Cloud cover thus plays an important role in the energetic balance of the atmosphere and a variation of it is a consequence of and to the climate change expected by recent studies.[3]


  1. ^ Ralph E. (1970) [1959]. "Cloud cover". Glossary of Meteorology (2nd ed.). Boston: American Meteorological Society. Retrieved August 24, 2013. 
  2. ^
  3. ^ IPCC Third Assessment Report Chapter 7. Physical Climate Processes and Feedbacks (Atmospheric Processes and Feedbacks 7.2) (Report). International Panel on Climate Change. Retrieved August 24, 2013. "It has extensive coverage of cloud-climate interactions"
  • McIntosh, D. H. (1972) Meteorological Glossary, Her Majesty's Stationery Office, Met. O. 842, A.P. 897, 319 p.

External links[edit]