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. For other uses, see Sky (disambiguation). ... hello--~~~~fake <gallery> poos[[kill]] </gallery> For other uses, see Cloud (disambiguation). ...

Measurement

Traditionally, cloud cover is estimated by trained observers from a meteorological station on the ground and expressed either in oktas (or eighths of the sky) or in tenths. These visual estimates are given to the closest value only. A value of 0 refers to clear sky, while 8 oktas or 10 on the decimal scale indicates overcast. Such estimates are representative of conditions within the range of visibility of the observer. The main problems associated with this method include the inability of making observations when visibility is very low (e.g., in case of fog) or the difficulties of estimating the correct fractional cover for clouds that are near the visual horizon. // Meteorology (from Greek: μετέωρον, meteoron, high in the sky; and λόγος, logos, knowledge) is the interdisciplinary scientific study of the atmosphere that focuses on weather processes and forecasting. ... In meteorology, an okta is a unit of measurement used to describe cloud cover. ... In Meteorology, ability is a measure of the nothingness at which an object or light can be seen. ...

With the advent of satellite observations, it has become possible to estimate the fractional cloud cover much more accurately (though not without difficulties). Identifying deep bright clouds on satellite images acquired in the solar spectrum is relatively easy. However, thin clouds or clouds with horizontal dimensions smaller than the spatial resolution of the sensor may largely escape detection. Earth observation satellites are satellites specifically designed to observe Earth from orbit, similar to reconnaissance satellites but intended for non-military uses such as environmental monitoring, meteorology, map making etc. ... Satellite imagery consists of photographs of Earth or other planets made from artificial satellites. ...

Role in the climate system

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). Climate is the average and variations of weather over long periods of time. ... Sol redirects here. ... In most modern usages of the word spectrum, there is a unifying theme of between extremes at either end. ... Top: Increasing atmospheric CO2 levels as measured in the atmosphere and ice cores. ...

See climate change for a more detailed discussion of these issues. Variations in CO2, temperature and dust from the Vostok ice core over the last 450,000 years For current global climate change, see Global warming. ...

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

Wikimedia Commons has media related to:

Cloud cover

• Glossary of Atmospheric Terms, http://www.nsdl.arm.gov/Library/glossary.shtml#Cloud_cover : From the National Science Digital Library's Atmospheric Visualization Collection.