Editing Sea surface temperature (section)

===Tropical cyclones===
[[File:WorldwideTCpeaks.gif|thumb|right|Seasonal peaks of tropical cyclone activity worldwide]]
[[File:Mean sst equatorial pacific.gif|thumb|right|200 px|Average equatorial Pacific temperatures]]
{{Main|Tropical cyclogenesis|Tropical cyclones and climate change}}
Ocean temperature of at least 26.5[[degrees Celsius|°C]] (79.7[[degrees Fahrenheit|°F]]) spanning through at minimum a 50-[[metre]] depth is one of the precursors needed to maintain a [[tropical cyclone]] (a type of [[mesocyclone]]).<ref name="A15">{{cite web|author=Chris Landsea|url=http://www.aoml.noaa.gov/hrd/tcfaq/A15.html|title=Subject: A15) How do tropical cyclones form?|access-date=2011-01-27|year=2011|publisher=[[Hurricane Research Division]]|author-link=Chris Landsea}}</ref><ref name=SST>{{cite journal|last=Webster|first=PJ|title=Changes in tropical cyclone number, duration, and intensity in a warming environment|journal=Science|volume=309|issue=5742|pages=1844–6|url=http://go.galegroup.com/ps/i.do?id=GALE%7CA136847986&v=2.1&it=r&p=PROF&sw=w&asid=335992f2037df3339c5901f7981d2045|publisher=Gale Group|pmid=16166514|year=2005|doi=10.1126/science.1116448|bibcode=2005Sci...309.1844W|doi-access=free}}</ref>  These warm waters are needed to maintain the [[Tropical cyclone#Mechanics|warm core]] that fuels tropical systems. This value is well above 16.1&nbsp;°C (60.9&nbsp;°F), the long term global average surface temperature of the oceans.<ref name="SSTMEAN">{{Cite web| author = Matt Menne | publisher = [[National Climatic Data Center]] | url = http://www.ncdc.noaa.gov/cmb-faq/anomalies.php#mean | title = Global Long-term Mean Land and Sea Surface Temperatures | date = March 15, 2000 | access-date = 2006-10-19}}</ref> However, this requirement can be considered only a general baseline because it assumes that the ambient atmospheric environment surrounding an area of disturbed weather presents average conditions. Tropical cyclones have intensified when SSTs were slightly below this standard temperature.

Tropical cyclones are known to form even when normal conditions are not met. For example, cooler air temperatures at a higher altitude (e.g., at the 500&nbsp;[[hPa]] level, or 5.9&nbsp;km) can lead to tropical cyclogenesis at lower water temperatures, as a certain [[lapse rate]] is required to force the atmosphere to be [[Baroclinic instability|unstable]] enough for convection. In a moist atmosphere, this lapse rate is 6.5&nbsp;°C/km, while in an atmosphere with less than 100% [[relative humidity]], the required lapse rate is 9.8&nbsp;°C/km.<ref name="TCS EESC">{{cite web|year=2000|last=Kushnir|first=Yochanan|title=The Climate System|url=http://eesc.columbia.edu/courses/ees/climate/lectures/atm_phys.html|publisher=[[Columbia University]]|access-date=24 September 2010|archive-date=20 May 2020|archive-url=https://web.archive.org/web/20200520171925/https://eesc.columbia.edu/courses/ees/climate/lectures/atm_phys.html|url-status=dead}}</ref>

At the 500&nbsp;hPa level, the air temperature averages −7&nbsp;°C (18&nbsp;°F) within the tropics, but air in the tropics is normally dry at this height, giving the air room to [[Wet-bulb temperature|wet-bulb]], or cool as it moistens, to a more favorable temperature that can then support convection. A [[wet-bulb temperature]] at 500&nbsp;hPa in a tropical atmosphere of {{convert|-13.2|C|F}} is required to initiate convection if the water temperature is {{convert|26.5|C|F}}, and this temperature requirement increases or decreases proportionally by 1&nbsp;°C in the sea surface temperature for each 1&nbsp;°C change at 500&nbsp;hpa.
Inside a [[cold-core low|cold cyclone]], 500&nbsp;hPa temperatures can fall as low as {{convert|-30|C|F}}, which can initiate convection even in the driest atmospheres. This also explains why moisture in the mid-levels of the [[troposphere]], roughly at the 500&nbsp;hPa level, is normally a requirement for development. However, when dry air is found at the same height, temperatures at 500&nbsp;hPa need to be even colder as dry atmospheres require a greater lapse rate for instability than moist atmospheres.<ref>{{cite book|title=Atmospheric Science: An Introductory Survey|author1=John M. Wallace  |author2=Peter V. Hobbs |name-list-style=amp |pages=76–77|publisher=Academic Press, Inc|year=1977}}</ref><ref name="LANDSEACLI">{{Cite web| author = Chris Landsea | url = http://www.aoml.noaa.gov/hrd/Landsea/climvari/index.html | title = Climate Variability of Tropical Cyclones: Past, Present and Future | year = 2000 | work = Storms | pages = 220–41 | access-date = 2006-10-19 | publisher = [[Atlantic Oceanographic and Meteorological Laboratory]]| author-link = Chris Landsea}}</ref> At heights near the [[tropopause]], the 30-year average temperature (as measured in the period encompassing 1961 through 1990) was −77&nbsp;°C (−132&nbsp;°F).<ref name="UAIRtropics">{{Cite journal| author = Dian J. Gaffen-Seidel, Rebecca J. Ross and James K. Angell | title = Climatological characteristics of the tropical tropopause as revealed by radiosondes | journal = Journal of Geophysical Research | volume = 106 | issue = D8 | pages = 7857–7878 | url = http://www.aero.jussieu.fr/~sparc/SPARC2000_new/OralSess2/D_Gaffen/GaffenHtml/Abs_Gaffen.html |date = November 2000| access-date = 2006-10-19 |archive-url = https://web.archive.org/web/20060508184913/http://www.aero.jussieu.fr/~sparc/SPARC2000_new/OralSess2/D_Gaffen/GaffenHtml/Abs_Gaffen.html |archive-date = May 8, 2006| bibcode = 2001JGR...106.7857S | doi = 10.1029/2000JD900837 | doi-access = free}}</ref> One example of a [[tropical cyclone]] maintaining itself over cooler waters was [[Hurricane Epsilon (2005)|Epsilon]] late in the [[2005 Atlantic hurricane season]].<ref>{{cite web|author=Lixion Avila|date=2005-12-03|title=Hurricane Epsilon Discussion Eighteen|publisher=National Hurricane Center|access-date=2010-12-14|url=http://www.nhc.noaa.gov/archive/2005/dis/al292005.discus.018.shtml?}}</ref>