Editing Convection (section)

===Oceanic circulation===
{{Main|Gulf Stream|Thermohaline circulation}}
[[File:Conveyor belt.svg|Ocean currents|thumb|200px|right]]

Solar radiation affects the oceans: warm water from the Equator tends to circulate toward the [[geographical pole|pole]]s, while cold polar water heads towards the Equator.  The surface currents are initially dictated by surface wind conditions.  The [[trade winds]] blow westward in the tropics,<ref>{{cite web |title=trade winds |work=Glossary of Meteorology |publisher=American Meteorological Society |year=2009 |access-date=2008-09-08 |url=http://amsglossary.allenpress.com/glossary/search?id=trade-winds1 |url-status=dead |archive-url=https://web.archive.org/web/20081211050708/http://amsglossary.allenpress.com/glossary/search?id=trade-winds1 |archive-date=2008-12-11 }}</ref> and the [[westerlies]] blow eastward at mid-latitudes.<ref>Glossary of Meteorology (2009). [http://amsglossary.allenpress.com/glossary/search?id=westerlies1 Westerlies.] {{webarchive|url=https://web.archive.org/web/20100622073904/http://amsglossary.allenpress.com/glossary/search?id=westerlies1 |date=2010-06-22 }} [[American Meteorological Society]]. Retrieved on 2009-04-15.</ref>  This wind pattern applies a [[stress (physics)|stress]] to the subtropical ocean surface with negative [[curl (mathematics)|curl]] across the [[Northern Hemisphere]],<ref>Matthias Tomczak and J. Stuart Godfrey (2001). [http://www.es.flinders.edu.au/~mattom/regoc/pdffiles/colour/double/04P-Ekman-left.pdf Regional Oceanography: an Introduction.] {{webarchive|url=https://web.archive.org/web/20090914120630/http://www.es.flinders.edu.au/~mattom/regoc/pdffiles/colour/double/04P-Ekman-left.pdf |date=2009-09-14 }} Matthias Tomczak, pp. 42. {{ISBN|81-7035-306-8}}. Retrieved on 2009-05-06.</ref> and the reverse across the [[Southern Hemisphere]].  The resulting [[Sverdrup transport]] is equatorward.<ref>Earthguide (2007). [http://earthguide.ucsd.edu/parkerprogram/berger/pdf/OcnBasLesson06.pdf Lesson 6: Unraveling the Gulf Stream Puzzle - On a Warm Current Running North.] {{webarchive|url=https://web.archive.org/web/20080723104316/http://earthguide.ucsd.edu/parkerprogram/berger/pdf/OcnBasLesson06.pdf |date=2008-07-23 }} [[University of California]] at San Diego. Retrieved on 2009-05-06.</ref>  Because of conservation of [[potential vorticity]] caused by the poleward-moving winds on the [[subtropical ridge]]'s western periphery and the increased relative vorticity of poleward moving water, transport is balanced by a narrow, accelerating poleward current, which flows along the western boundary of the ocean basin, outweighing the effects of friction with the cold western boundary current which originates from high latitudes.<ref>Angela Colling (2001). [https://books.google.com/books?id=tFJRLhSez_YC&pg=PA90 Ocean circulation.] {{webarchive|url=https://web.archive.org/web/20180302144439/https://books.google.com/books?id=tFJRLhSez_YC&pg=PA90 |date=2018-03-02 }} Butterworth-Heinemann, pp. 96. Retrieved on 2009-05-07.</ref>  The overall process, known as western intensification, causes currents on the western boundary of an ocean basin to be stronger than those on the eastern boundary.<ref>National Environmental Satellite, Data, and Information Service (2009). [http://www.science-house.org/nesdis/gulf/background.html Investigating the Gulf Stream.] {{webarchive|url=https://web.archive.org/web/20100503013457/http://www.science-house.org/nesdis/gulf/background.html |date=2010-05-03 }} [[North Carolina State University]]. Retrieved on 2009-05-06.</ref>

As it travels poleward, warm water transported by strong warm water current undergoes evaporative cooling. The cooling is wind driven: wind moving over water cools the water and also causes [[evaporation]], leaving a saltier brine. In this process, the water becomes saltier and denser and decreases in temperature.  Once sea ice forms, salts are left out of the ice, a process known as brine exclusion.<ref>{{cite web |last=Russel |first=Randy |title=Thermohaline Ocean Circulation |url=http://www.windows.ucar.edu/tour/link=/earth/Water/thermohaline_ocean_circulation.html |publisher=University Corporation for Atmospheric Research |access-date=2009-01-06 |url-status=live |archive-url=https://web.archive.org/web/20090325062339/http://www.windows.ucar.edu/tour/link=/earth/Water/thermohaline_ocean_circulation.html |archive-date=2009-03-25 }}</ref>  These two processes produce water that is denser and colder.  The water across the northern [[Atlantic Ocean]] becomes so dense that it begins to sink down through less salty and less dense water. (This [[open ocean convection]] is not unlike that of a [[lava lamp]].) This downdraft of heavy, cold and dense water becomes a part of the [[North Atlantic Deep Water]], a south-going stream.<ref>{{cite web |last=Behl |first=R. |title=Atlantic Ocean water masses |url=http://seis.natsci.csulb.edu/rbehl/NADW.htm |publisher=[[California State University]] Long Beach |access-date=2009-01-06|archive-url = https://web.archive.org/web/20080523170145/http://seis.natsci.csulb.edu/rbehl/NADW.htm |archive-date = May 23, 2008|url-status=dead}}</ref>
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