Editing Convection (section)

===Atmospheric convection===
{{main|Atmospheric convection}}

====Atmospheric circulation====
{{main|Atmospheric circulation}}
[[File:Earth Global Circulation.jpg|thumb|300px|left|Idealised depiction of the global circulation on Earth]]

'''Atmospheric circulation''' is the large-scale movement of air, and is a means by which [[thermal energy]] is distributed on the surface of the [[Earth]], together with the much slower (lagged) ocean circulation system. The large-scale structure of the [[atmospheric circulation]] varies from year to year, but the basic climatological structure remains fairly constant.

Latitudinal circulation occurs because incident solar [[radiation]] per unit area is highest at the [[heat equator]], and decreases as the [[latitude]] increases, reaching minima at the poles. It consists of two primary convection cells, the [[Hadley cell]] and the [[polar vortex]], with the [[Hadley cell]] experiencing stronger convection due to the release of [[latent heat]] energy by [[condensation]] of [[water vapor]] at higher altitudes during cloud formation.

Longitudinal circulation, on the other hand, comes about because the [[ocean]] has a higher specific heat capacity than land (and also [[thermal conductivity]], allowing the heat to penetrate further beneath the surface ) and thereby absorbs and releases more [[heat]], but the [[temperature]] changes less than land. This brings the sea breeze, air cooled by the water, ashore in the day, and carries the land breeze, air cooled by contact with the ground, out to sea during the night. Longitudinal circulation consists of two cells, the [[Walker circulation]] and [[El Niño-Southern Oscillation|El Niño / Southern Oscillation]].
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====Weather====
{{see also|Cloud|Thunderstorm|Wind}}
[[File:foehn1.svg|right|thumb|300px|How Foehn is produced]]

Some more localized phenomena than global atmospheric movement are also due to convection, including wind and some of the [[hydrologic cycle]]. For example, a [[foehn wind]] is a down-slope wind which occurs on the downwind side of a mountain range. It results from the [[adiabatic]] warming of air which has dropped most of its moisture on windward slopes.<ref name="MT">{{cite web|first=Michael|last=Pidwirny|year=2008|url=http://www.physicalgeography.net/fundamentals/8e.html|title=CHAPTER 8: Introduction to the Hydrosphere (e). Cloud Formation Processes|publisher=Physical Geography|access-date=2009-01-01|url-status=dead|archive-url=https://web.archive.org/web/20081220230524/http://www.physicalgeography.net/fundamentals/8e.html|archive-date=2008-12-20}}</ref> Because of the different adiabatic lapse rates of moist and dry air, the air on the leeward slopes becomes warmer than at the same height on the windward slopes.

A [[thermal column]] (or thermal) is a vertical section of rising air in the lower altitudes of the Earth's atmosphere. Thermals are created by the uneven heating of the Earth's surface from solar radiation. The Sun warms the ground, which in turn warms the air directly above it. The warmer air expands, becoming less dense than the surrounding air mass, and creating a [[thermal low]].<ref>{{cite web|agency=National Weather Service Forecast Office in [[Tucson, Arizona]]|year=2008|url=http://www.wrh.noaa.gov/twc/monsoon/monsoon_whatis.php|title=What is a monsoon?|publisher=National Weather Service Western Region Headquarters|access-date=2009-03-08|url-status=live|archive-url=https://web.archive.org/web/20120623140647/http://www.wrh.noaa.gov/twc/monsoon/monsoon_whatis.php|archive-date=2012-06-23}}</ref><ref>{{cite journal|first1 = Douglas G. | last1 = Hahn | author2-link = Syukuro Manabe | first2 = Syukuro | last2 = Manabe |year=1975|bibcode=1975JAtS...32.1515H|title=The Role of Mountains in the South Asian Monsoon Circulation|journal=[[Journal of the Atmospheric Sciences]]|volume=32|issue=8|pages=1515–1541|doi=10.1175/1520-0469(1975)032<1515:TROMIT>2.0.CO;2|issn=1520-0469|doi-access=free}}</ref> The mass of lighter air rises, and as it does, it cools by expansion at lower air pressures. It stops rising when it has cooled to the same temperature as the surrounding air. Associated with a thermal is a downward flow surrounding the thermal column. The downward moving exterior is caused by colder air being displaced at the top of the thermal. Another convection-driven weather effect is the [[sea breeze]].<ref>University of Wisconsin. [http://cimss.ssec.wisc.edu/wxwise/seabrz.html Sea and Land Breezes.] {{webarchive|url=https://web.archive.org/web/20120704184333/http://cimss.ssec.wisc.edu/wxwise/seabrz.html |date=2012-07-04 }} Retrieved on 2006-10-24.</ref><ref name="Jet">JetStream:  An Online School For Weather (2008). [http://www.srh.weather.gov/srh/jetstream/ocean/seabreezes.htm The Sea Breeze.] {{webarchive|url=https://web.archive.org/web/20060923233344/http://www.srh.weather.gov/srh/jetstream/ocean/seabreezes.htm |date=2006-09-23 }} [[National Weather Service]]. Retrieved on 2006-10-24.</ref>

[[File:Thunderstorm formation.jpg|thumb|500px|Stages of a thunderstorm's life.]]
Warm air has a lower density than cool air, so warm air rises within cooler air,<ref>{{cite book|url=https://books.google.com/books?id=PDtIAAAAIAAJ&pg=PA462 |title=Civil engineers' pocket book: a reference-book for engineers, contractors|first = Albert Irvin | last = Frye|page=462|publisher=D. Van Nostrand Company|year=1913|access-date=2009-08-31}}</ref> similar to [[hot air balloon]]s.<ref>{{cite book
| url = https://books.google.com/books?id=ssO_19TRQ9AC&q=Kongming+balloon&pg=PA112
| title = Ancient Chinese Inventions
| first = Yikne | last = Deng
| publisher = Chinese International Press
| isbn=978-7-5085-0837-5
| year=2005
| pages = 112–13
| access-date = 2009-06-18}}</ref>  Clouds form as relatively warmer air carrying moisture rises within cooler air. As the moist air rises, it cools, causing some of the [[water vapor]] in the rising packet of air to [[condensation|condense]].<ref>{{cite web|agency=FMI|year=2007|url=http://www.zamg.ac.at/docu/Manual/SatManu/main.htm?/docu/Manual/SatManu/CMs/FgStr/backgr.htm|title=Fog And Stratus – Meteorological Physical Background|publisher=Zentralanstalt für Meteorologie und Geodynamik|access-date=2009-02-07|url-status=live|archive-url=https://web.archive.org/web/20110706085616/http://www.zamg.ac.at/docu/Manual/SatManu/main.htm?%2Fdocu%2FManual%2FSatManu%2FCMs%2FFgStr%2Fbackgr.htm|archive-date=2011-07-06}}</ref>  When the moisture condenses, it releases energy known as [[latent heat]] of condensation which allows the rising packet of air to cool less than its surrounding air,<ref>{{cite book|url=https://books.google.com/books?id=RRSzR4NQdGkC&pg=PA20 |title=Storm world: hurricanes, politics, and the battle over global warming| first = Chris C. | last = Mooney|page=20|isbn=978-0-15-101287-9|publisher=Houghton Mifflin Harcourt|year=2007|access-date=2009-08-31}}</ref> continuing the cloud's ascension. If enough [[Convective available potential energy|instability]] is present in the atmosphere, this process will continue long enough for [[Cumulonimbus|cumulonimbus clouds]] to form, which support lightning and thunder. Generally, thunderstorms require three conditions to form: moisture, an unstable airmass, and a lifting force (heat).

All [[thunderstorm]]s, regardless of type, go through three stages: the '''developing stage''', the '''mature stage''', and the '''dissipation stage'''.<ref name="Extreme Weather">{{cite book |title=Extreme Weather |first=Michael H. |last=Mogil |year=2007 |publisher=Black Dog & Leventhal Publisher |location=New York |isbn=978-1-57912-743-5 |pages=[https://archive.org/details/extremeweatherun0000mogi/page/210 210–211] |url=https://archive.org/details/extremeweatherun0000mogi/page/210 }}</ref> The average thunderstorm has a {{convert|24|km|mi|abbr=on}} diameter. Depending on the conditions present in the atmosphere, these three stages take an average of 30 minutes to go through.<ref name="tsbasics">{{cite web|url=http://www.nssl.noaa.gov/primer/tstorm/tst_basics.html|title=A Severe Weather Primer: Questions and Answers about Thunderstorms|agency=National Severe Storms Laboratory|publisher=[[National Oceanic and Atmospheric Administration]]|date=2006-10-15|access-date=2009-09-01|url-status=dead|archive-url=https://web.archive.org/web/20090825000832/http://www.nssl.noaa.gov/primer/tstorm/tst_basics.html|archive-date=2009-08-25}}</ref>