Sea surface temperature#Tropical cyclones

{{See also|Ocean temperature}}

File:SST 20131220 blended Global.png

Sea surface temperature (SST), or ocean surface temperature, is the water temperature close to the ocean's surface. The exact meaning of surface varies according to the measurement method used, but it is between {{convert|1|mm|in|sigfig=1}} and {{convert|20|m|ft|sigfig=1}} below the sea surface.

For comparison, the sea surface skin temperature relates to the top 20 or so micrometres of the ocean's surface.

The definition proposed by Intergovernmental Panel on Climate Change (IPCC) for sea surface temperature does not specify the number of metres but focuses more on measurement techniques: Sea surface temperature is "the subsurface bulk temperature in the top few metres of the ocean, measured by ships, buoys and drifters. [...] Satellite measurements of skin temperature (uppermost layer; a micrometre thick) in the infrared or the top centimetre or so in the microwave are also used, but must be adjusted to be compatible with the bulk temperature."IPCC, 2021: [https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_AnnexVII.pdf Annex VII: Glossary] [Matthews, J.B.R., V. Möller, R. van Diemen, J.S. Fuglestvedt, V. Masson-Delmotte, C. Méndez, S. Semenov, A. Reisinger (eds.)]. In [https://www.ipcc.ch/report/ar6/wg1/ Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change] [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 2215–2256, doi:10.1017/9781009157896.022.{{rp|2248}}

The temperature further below that is called ocean temperature or deeper ocean temperature. Ocean temperatures (more than 20 metres below the surface) also vary by region and time, and they contribute to variations in ocean heat content and ocean stratification. The increase of both ocean surface temperature and deeper ocean temperature is an important effect of climate change on oceans.

{{See also|Ocean stratification|Photic zone}}

The extent of the ocean surface down into the ocean is influenced by the amount of mixing that takes place between the surface water and the deeper water. This depends on the temperature: in the tropics the warm surface layer of about 100 m is quite stable and does not mix much with deeper water, while near the poles winter cooling and storms makes the surface layer denser and it mixes to great depth and then stratifies again in summer. This is why there is no simple single depth for ocean surface. The photic depth of the ocean is typically about 100 m and is related to this heated surface layer. It can be up to around 200 m deep in the open ocean.{{Cite book |last1=Emerson |first1=Steven |url=https://www.cambridge.org/core/product/identifier/9780511793202/type/book |title=Chemical Oceanography and the Marine Carbon Cycle |last2=Hedges |first2=John |date=2008-04-24 |publisher=Cambridge University Press |isbn=978-0-521-83313-4 |edition=1 |chapter=Chapter 4: Carbonate chemistry |doi=10.1017/cbo9780511793202}}{{Cite book |last1=Chester |first1=R. |url=https://www.wiley.com/en-us/Marine+Geochemistry%2C+3rd+Edition-p-9781118349090 |title=Marine geochemistry |last2=Jickells |first2=Tim |date=2012 |publisher=Wiley/Blackwell |isbn=978-1-118-34909-0 |edition=3rd |location=Chichester, West Sussex, UK |chapter=Chapter 9: Nutrients, oxygen, organic carbon and the carbon cycle in seawater |oclc=781078031}}

File:ECCO2 Sea Surface Temperature and Flows.ogv

{{See also|Upwelling}}

The sea surface temperature (SST) has a diurnal range, just like the Earth's atmosphere above, though to a lesser degree due to its greater thermal inertia.{{cite book|url=https://books.google.com/books?id=WdPg_1aTtr8C&pg=PA84|page=84|author=John Siegenthaler|title=Modern hydronic heating for residential and light commercial buildings|year=2003|publisher=Cengage Learning|isbn=978-0-7668-1637-4}} On calm days, the temperature can vary by {{convert|6|C-change|F-change|sigfig=1}}. The temperature of the ocean at depth lags the Earth's atmosphere temperature by 15 days per {{convert|10|m|ft}}, which means for locations like the Aral Sea, temperatures near its bottom reach a maximum in December and a minimum in May and June.{{cite book|url=https://books.google.com/books?id=Z-LxfJVFclgC&pg=PA27|title=Physical oceanography of the dying Aral Sea|author=Peter O. Zavialov|page=27|year=2005|isbn=978-3-540-22891-2|publisher=シュプリンガー・ジャパン株式会社}} Near the coastline, some offshore and longshore winds move the warm waters near the surface offshore, and replace them with cooler water from below in the process known as Ekman transport. This pattern generally increases nutrients for marine life in the region, and can have a profound effect in some regions where the bottom waters are particularly nutrient-rich.{{cite web | title =Envisat watches for La Niña | publisher =BNSC via the Internet Wayback Machine | date =2008-04-24 | url =http://www.bnsc.gov.uk/content.aspx?nid=5989 | access-date =2011-01-09 |archive-url = https://web.archive.org/web/20080424113710/http://www.bnsc.gov.uk/content.aspx?nid=5989 |archive-date = 2008-04-24}} Offshore of river deltas, freshwater flows over the top of the denser seawater, which allows it to heat faster due to limited vertical mixing.{{cite book|url=https://books.google.com/books?id=OeZ4e5MwRigC&pg=PA258|page=258|title=State and evolution of the Baltic Sea, 1952–2005: a detailed 50-year survey of meteorology and climate, physics, chemistry, biology, and marine environment|year=2008|publisher=John Wiley and Sons|isbn=978-0-471-97968-5|author1=Rainer Feistel |author2=Günther Nausch |author3=Norbert Wasmund}} Remotely sensed SST can be used to detect the surface temperature signature due to tropical cyclones. In general, an SST cooling is observed after the passing of a hurricane, primarily as the result of mixed layer deepening and surface heat losses.{{cite web|author=Earth Observatory |url=http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17164 |title=Passing of Hurricanes Cools Entire Gulf |year=2005 |access-date=2006-04-26 |publisher=National Aeronautics and Space Administration |url-status=dead |archive-url=https://web.archive.org/web/20060930235454/http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17164 |archive-date=2006-09-30}} In the wake of several day long Saharan dust outbreaks across the adjacent northern Atlantic Ocean, sea surface temperatures are reduced 0.2 C to 0.4 C (0.3 to 0.7 F).{{cite book|url=https://books.google.com/books?id=b09YTtIW3f4C&pg=PA72|title=The Impact of Saharan Dust on the North Atlantic Circulation|author=Nidia Martínez Avellaneda|page=72|year=2010|publisher=GRIN Verlag|isbn=978-3-640-55639-7}} Other sources of short-term SST fluctuation include extratropical cyclones, rapid influxes of glacial fresh water{{cite journal|last=Boyle|first=Edward A.|author2=Lloyd Keigwin |title=North Atlantic thermohaline circulation during the past 20,000 years linked to high-latitude surface temperature|journal=Nature|date=5 November 1987|volume=330|issue=6143|pages=35–40|url=http://www.whoi.edu/cms/files/Boyle(1987)Nature330_35_52423.pdf|access-date=10 February 2011|doi=10.1038/330035a0|bibcode = 1987Natur.330...35B |s2cid=4359752}} and concentrated phytoplankton blooms{{cite journal|last=Beaugrand|first=Grégory|author2=Keith M. Brander |author3=J. Alistair Lindley |author4=Sami Souissi |author5=Philip C. Reid |title=Plankton effect on cod recruitment in the North Sea|journal=Nature|date=11 December 2003|volume=426|pages=661–664|doi=10.1038/nature02164|issue=6967|pmid=14668864|bibcode = 2003Natur.426..661B |s2cid=4420759}} due to seasonal cycles or agricultural run-off.{{cite journal|last=Beman|first=J. Michael |author2=Kevin R. Arrigo |author3=Pamela A. Matson|title=Agricultural runoff fuels large phytoplankton blooms in vulnerable areas of the ocean|journal=Nature|date=10 March 2005|volume=434|pages=211–214|doi=10.1038/nature03370|issue=7030|pmid=15758999|bibcode = 2005Natur.434..211M |s2cid=2299664}}{{clarify|What effects do algal blooms have on SST?|date=January 2022}}

The tropical ocean has been warming faster than other regions since 1950, with the greatest rates of warming in the tropical Indian Ocean, western Pacific Ocean, and western boundary currents of the subtropical gyres. However, the eastern Pacific Ocean, subtropical North Atlantic Ocean, and Southern Ocean have warmed more slowly than the global average or have experienced cooling since the 1950s.

Ocean currents, such as the Atlantic Multidecadal Oscillation, can affect sea surface temperatures over several decades.{{Cite journal |last1=McCarthy |first1=Gerard D. |last2=Haigh |first2=Ivan D. |last3=Hirschi |first3=Joël J.-M. |last4=Grist |first4=Jeremy P. |last5=Smeed |first5=David A. |date=2015-05-28 |title=Ocean impact on decadal Atlantic climate variability revealed by sea-level observations |url=http://mural.maynoothuniversity.ie/12187/1/McCarthy_Ocean_2015.pdf |journal=Nature |volume=521 |issue=7553 |pages=508–510 |bibcode=2015Natur.521..508M |doi=10.1038/nature14491 |issn=1476-4687 |pmid=26017453 |s2cid=4399436}} The Atlantic Multidecadal Oscillation (AMO) is an important driver of North Atlantic SST and Northern Hemisphere climate, but the mechanisms controlling AMO variability remain poorly understood.{{Cite journal |last1=Knudsen |first1=Mads Faurschou |last2=Jacobsen |first2=Bo Holm |last3=Seidenkrantz |first3=Marit-Solveig |last4=Olsen |first4=Jesper |date=2014-02-25 |title=Evidence for external forcing of the Atlantic Multidecadal Oscillation since termination of the Little Ice Age |journal=Nature Communications |volume=5 |pages=3323 |bibcode=2014NatCo...5.3323K |doi=10.1038/ncomms4323 |issn=2041-1723 |pmc=3948066 |pmid=24567051}} Atmospheric internal variability, changes in ocean circulation, or anthropogenic drivers may control the multidecadal temperature variability associated with AMO.{{Cite journal |last1=Wills |first1=R.C. |last2=Armour |first2=K.C. |last3=Battisti |first3=D.S. |last4=Hartmann |first4=D.L. |date=2019 |title=Ocean–atmosphere dynamical coupling fundamental to the Atlantic multidecadal oscillation |journal=Journal of Climate |volume=32 |issue=1 |pages=251–272|doi=10.1175/JCLI-D-18-0269.1 |bibcode=2019JCli...32..251W |s2cid=85450306 |doi-access=free}} These changes in North Atlantic SST may influence winds in the subtropical North Pacific and produce warmer SSTs in the western Pacific Ocean.{{Cite journal |last1=Wu |first1=Baolan |last2=Lin |first2=Xiaopei |last3=Yu |first3=Lisan |date=17 February 2020 |title=North Pacific subtropical mode water is controlled by the Atlantic Multidecadal Variability |url=https://www.nature.com/articles/s41558-020-0692-5 |journal=Nature Climate Change |language=en |volume=10 |issue=3 |pages=238–243 |doi=10.1038/s41558-020-0692-5 |bibcode=2020NatCC..10..238W |s2cid=211138572 |issn=1758-6798}}File:Weeklysst.gif.]]

File:1997 El Nino TOPEX.jpg. The white areas off the tropical coasts of South and North America indicate the pool of warm water.{{cite web | url = http://www.jpl.nasa.gov/news/releases/97/elninoup.html | title =Independent NASA Satellite Measurements Confirm El Niño is Back and Strong | publisher = NASA/JPL}}]]

{{Main|El Niño-Southern Oscillation}}

El Niño is defined by prolonged differences in Pacific Ocean surface temperatures when compared with the average value. The accepted definition is a warming or cooling of at least 0.5 °C (0.9 °F) averaged over the east-central tropical Pacific Ocean. Typically, this anomaly happens at irregular intervals of 2–7 years and lasts nine months to two years.{{cite web|url=http://www.cpc.noaa.gov/products/analysis_monitoring/ensostuff/ensofaq.shtml#HOWOFTEN|title=ENSO FAQ: How often do El Niño and La Niña typically occur?|access-date=2009-07-26|date=2005-12-19|author=Climate Prediction Center|publisher=National Centers for Environmental Prediction|author-link=Climate Prediction Center|archive-url=https://web.archive.org/web/20090827143632/http://www.cpc.noaa.gov/products/analysis_monitoring/ensostuff/ensofaq.shtml#HOWOFTEN|archive-date=2009-08-27|url-status=dead}} The average period length is 5 years. When this warming or cooling occurs for only seven to nine months, it is classified as El Niño/La Niña "conditions"; when it occurs for more than that period, it is classified as El Niño/La Niña "episodes".{{cite web|url=http://www.ncdc.noaa.gov/oa/climate/research/enso/?year=2009&month=6&submitted=true|title=El Niño / Southern Oscillation (ENSO) June 2009|author=National Climatic Data Center|publisher=National Oceanic and Atmospheric Administration|date=June 2009|access-date=2009-07-26|author-link=National Climatic Data Center}}

The sign of an El Niño in the sea surface temperature pattern is when warm water spreads from the west Pacific and the Indian Ocean to the east Pacific. It takes the rain with it, causing extensive drought in the western Pacific and rainfall in the normally dry eastern Pacific. El Niño's warm rush of nutrient-poor tropical water, heated by its eastward passage in the Equatorial Current, replaces the cold, nutrient-rich surface water of the Humboldt Current. When El Niño conditions last for many months, extensive ocean warming and the reduction in Easterly Trade winds limits upwelling of cold nutrient-rich deep water and its economic impact to local fishing for an international market can be serious.{{cite web|url=http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/eln/home.rxml|title=El Niño|date=1998-04-28|access-date=2009-07-17|author=WW2010|publisher=University of Illinois at Urbana-Champaign}}

Among scientists, there is medium confidence that the tropical Pacific will transition to a mean pattern resembling that of El Niño on centennial time scale, but there is still high uncertainty in tropical Pacific SST projections because it is difficult to capture El Niño variability in climate models.File:Land vs Ocean Temperature.svg

File:1880- Global average sea surface temperature - global warming.svg

{{Further|Effects of climate change on oceans#Rising ocean temperature}}

Overall, scientists project that all regions of the oceans will warm by 2050, but models disagree for SST changes expected in the subpolar North Atlantic, the equatorial Pacific, and the Southern Ocean. The future global mean SST increase for the period 1995-2014 to 2081-2100 is 0.86 °C under the most modest greenhouse gas emissions scenarios, and up to 2.89 °C under the most severe emissions scenarios.

A study published in 2025 in Environmental Research Letters reported that global mean sea surface temperature increases had more than quadrupled, from 0.06{{nbsp}}K per decade during 1985–89 to 0.27{{nbsp}}K per decade for 2019–23. The researchers projected that the increase inferred over the past 40 years would likely be exceeded within the next 20 years.{{cite journal |last1=Merchant |first1=Christopher J. |last2=Allan |first2=Richard P. |last3=Embury |first3=Owen |title=Quantifying the acceleration of multidecadal global sea surface warming driven by Earth's energy imbalance |journal=Environmental Research Letters |date=28 January 2025 |volume=20 |issue=2 |page=024037 |doi=10.1088/1748-9326/adaa8a|doi-access=free |bibcode=2025ERL....20b4037M }}

File:MODIS and AIRS SST comp fig2.i.jpg

There are a variety of techniques for measuring this parameter that can potentially yield different results because different things are actually being measured. Away from the immediate sea surface, general temperature measurements are accompanied by a reference to the specific depth of measurement. This is because of significant differences encountered between measurements made at different depths, especially during the daytime when low wind speed and high sunshine conditions may lead to the formation of a warm layer at the ocean's surface and strong vertical temperature gradients (a diurnal thermocline). Sea surface temperature measurements are confined to the top portion of the ocean, known as the near-surface layer.{{cite book|url=https://books.google.com/books?id=tZary8a4HMwC|page=xi|author1=Alexander Soloviev |author2=Roger Lukas |title=The near-surface layer of the ocean: structure, dynamics and applications|journal=The Near-Surface Layer of the Ocean: Structure|isbn=978-1-4020-4052-8|year=2006|publisher=シュプリンガー・ジャパン株式会社|bibcode=2006nslo.book.....S}}

The sea surface temperature was one of the first oceanographic variables to be measured. Benjamin Franklin suspended a mercury thermometer from a ship while travelling between the United States and Europe in his survey of the Gulf Stream in the late eighteenth century. SST was later measured by dipping a thermometer into a bucket of water that was manually drawn from the sea surface. The first automated technique for determining SST was accomplished by measuring the temperature of water in the intake port of large ships, which was underway by 1963. These observations have a warm bias of around {{convert|0.6|C-change|F-change|sigfig=1}} due to the heat of the engine room.{{cite book|url=https://books.google.com/books?id=A6ew-bJDIDIC&pg=PA24|pages=24–25|title=Data analysis methods in physical oceanography|author1=William J. Emery |author2=Richard E. Thomson |year=2001|isbn=978-0-444-50757-0|publisher=Elsevier|edition=2nd Revised}}

Fixed weather buoys measure the water temperature at a depth of {{convert|3|m|ft}}. Measurements of SST have had inconsistencies over the last 130 years due to the way they were taken. In the nineteenth century, measurements were taken in a bucket off a ship. However, there was a slight variation in temperature because of the differences in buckets. Samples were collected in either a wood or an uninsulated canvas bucket, but the canvas bucket cooled quicker than the wood bucket. The sudden change in temperature between 1940 and 1941 was the result of an undocumented change in procedure. The samples were taken near the engine intake because it was too dangerous to use lights to take measurements over the side of the ship at night.{{cite book|last=Burroughs|first=William James|title=Climate change : a multidisciplinary approach|url=https://archive.org/details/climatechangemul0000burr_p9v1|url-access=registration|year=2007|publisher=Cambridge Univiversity Press|location=Cambridge [u.a.]|isbn=9780521690331|edition=2.}}

Many different drifting buoys exist around the world that vary in design, and the location of reliable temperature sensors varies. These measurements are beamed to satellites for automated and immediate data distribution.{{cite book|url=https://books.google.com/books?id=hH2NkL_318wC&pg=PA263|pages=237–238|title=Oceanography from Space: Revisited|author=Vittorio Barale|year=2010|isbn=978-90-481-8680-8|publisher=Springer}} A large network of coastal buoys in U.S. waters is maintained by the National Data Buoy Center (NDBC).{{cite book|page=[https://archive.org/details/meteorologicalbu0000unse/page/11 11]|title=The meteorological buoy and coastal marine automated network for the United States|author=Lance F. Bosart, William A. Sprigg, National Research Council|publisher=National Academies Press|year=1998|isbn=978-0-309-06088-2|url=https://archive.org/details/meteorologicalbu0000unse/page/11}} Between 1985 and 1994, an extensive array of moored and drifting buoys was deployed across the equatorial Pacific Ocean designed to help monitor and predict the El Niño phenomenon.{{cite book|url=https://books.google.com/books?id=DO5K1NK_ZewC&pg=PA62|title=Global energy and water cycles|author1=K. A. Browning |author2=Robert J. Gurney |page=62|year=1999|publisher=Cambridge University Press|isbn=978-0-521-56057-3}}

{{See also|Weather satellite|Satellite temperature measurement}}

File:MODIS sst.png Aqua data]]

Weather satellites have been available to determine sea surface temperature information since 1967, with the first global composites created during 1970.{{cite journal|url=http://docs.lib.noaa.gov/rescue/mwr/100/mwr-100-01-0010.pdf|title=Global Sea-Surface Temperature Distribution Determined From an Environmental Satellite|author=P. Krishna Rao, W. L. Smith, and R. Koffler|pages=10–14|journal=Monthly Weather Review|volume=100|date=January 1972|access-date=2011-01-09|issue=1|doi=10.1175/1520-0493(1972)100<0010:GSTDDF>2.3.CO;2|bibcode = 1972MWRv..100...10K}} Since 1982,{{cite book|url=https://books.google.com/books?id=qzYrAAAAYAAJ&pg=PA2|page=2|author=National Research Council (U.S.). NII 2000 Steering Committee|title=The unpredictable certainty: information infrastructure through 2000; white papers|publisher=National Academies|year=1997|isbn=9780309060363}} satellites have been increasingly utilized to measure SST and have allowed its spatial and temporal variation to be viewed more fully. Satellite measurements of SST are in reasonable agreement with in situ temperature measurements.{{cite journal|journal=Journal of Geophysical Research|date=2001-02-15|volume=106|author1=W. J. Emery|author2=D. J. Baldwin|author3=Peter Schlüssel|author4=R. W. Reynolds|name-list-style=amp|title=Accuracy of in situ sea surface temperatures used to calibrate infrared satellite measurements|page=2387|issue=C2|bibcode=2001JGR...106.2387E|doi=10.1029/2000JC000246|doi-access=free}} The satellite measurement is made by sensing the ocean radiation in two or more wavelengths within the infrared part of the electromagnetic spectrum or other parts of the spectrum which can then be empirically related to SST.{{cite web|url=http://www2.hawaii.edu/~jmaurer/sst/|title=Infrared and microwave remote sensing of sea surface temperature (SST)|author=John Maurer|date=October 2002|publisher=University of Hawai{{okina}}i|access-date=2011-01-09}} These wavelengths are chosen because they are:

1. within the peak of the blackbody radiation expected from the Earth,{{cite journal|url=http://www.wamis.org/agm/pubs/agm8/Paper-4.pdf|page=73|journal=Satellite Remote Sensing and GIS Applications in Agricultural Meteorology|title=Meteorological Satellites|author=C. M. Kishtawal|date=2005-08-06|access-date=2011-01-27|archive-date=2020-02-15|archive-url=https://web.archive.org/web/20200215044026/http://www.wamis.org/agm/pubs/agm8/Paper-4.pdf|url-status=dead}} and
2. able to transmit adequately well through the atmosphere{{cite journal|journal=New Scientist|date=1971-09-16|title=Mapping the Atmosphere From Space|author= Robert Harwood|page=623|volume=51|issue=769}}

The satellite-measured SST provides both a synoptic view of the ocean and a high frequency of repeat views,{{cite book|page=510|url=https://books.google.com/books?id=Y0iX2z48qkUC&pg=PA509|author1=David E. Alexander |author2=Rhodes Whitmore Fairbridge |title=Encyclopedia of environmental science|year=1999|publisher=Springer|isbn=978-0-412-74050-3}} allowing the examination of basin-wide upper ocean dynamics not possible with ships or buoys. [http://www.nasa.gov/ NASA's] (National Aeronautic and Space Administration) [http://modis.gsfc.nasa.gov/ Moderate Resolution Imaging Spectroradiometer (MODIS)] SST satellites have been providing global SST data since 2000, available with a one-day lag. NOAA's [http://www.goes.noaa.gov/ GOES (Geostationary Orbiting Earth Satellites)] {{Webarchive|url=https://web.archive.org/web/20200817111624/http://www.goes.noaa.gov/ |date=2020-08-17 }} satellites are geo-stationary above the Western Hemisphere which enables them to deliver SST data on an hourly basis with only a few hours of lag time.

There are several difficulties with satellite-based absolute SST measurements. First, in infrared remote sensing methodology the radiation emanates from the top "skin" of the ocean, approximately the top 0.01 mm or less, which may not represent the bulk temperature of the upper meter of ocean due primarily to effects of solar surface heating during the daytime, reflected radiation, as well as sensible heat loss and surface evaporation. All these factors make it somewhat difficult to compare satellite data to measurements from buoys or shipboard methods, complicating ground truth efforts.{{cite book|url=https://books.google.com/books?id=jk1fIo51uwMC&pg=PA278|page=279|author=Ian Stuart Robinson|title=Measuring the oceans from space: the principles and methods of satellite oceanography|publisher=Springer|year=2004|isbn=978-3-540-42647-9}} Secondly, the satellite cannot look through clouds, creating a cool bias in satellite-derived SSTs within cloudy areas. However, passive microwave techniques can accurately measure SST and penetrate cloud cover. Within atmospheric sounder channels on weather satellites, which peak just above the ocean's surface, knowledge of the sea surface temperature is important to their calibration.

File:Snow Clouds in Korea.jpg]]

{{See also|Air mass|Numerical weather prediction|Precipitation (meteorology)|Effects of climate change on oceans}}

Sea surface temperature affects the behavior of the Earth's atmosphere above, so their initialization into atmospheric models is important. While sea surface temperature is important for tropical cyclogenesis, it is also important in determining the formation of sea fog and sea breezes.{{cite book|url=https://books.google.com/books?id=hH2NkL_318wC&pg=PA263|page=263|title=Oceanography from Space: Revisited|author=Vittorio Barale|year=2010|isbn=978-90-481-8680-8|publisher=Springer}} Heat from underlying warmer waters can significantly modify an air mass over distances as short as {{convert|35|km|mi}} to {{convert|40|km|mi}}.{{cite journal|author=Jun Inoue, Masayuki Kawashima, Yasushi Fujiyoshi and Masaaki Wakatsuchi|title=Aircraft Observations of Air-mass Modification Over the Sea of Okhotsk during Sea-ice Growth|issue=1|date=October 2005|doi=10.1007/s10546-004-3407-y|pages=111–129|issn=0006-8314|volume=117| journal=Boundary-Layer Meteorology|bibcode = 2005BoLMe.117..111I |s2cid=121768400}} For example, southwest of Northern Hemisphere extratropical cyclones, curved cyclonic flow bringing cold air across relatively warm water bodies can lead to narrow lake-effect snow (or sea effect) bands. Those bands bring strong localized precipitation, often in the form of snow, since large water bodies such as lakes efficiently store heat that results in significant temperature differences—larger than {{convert|13|C-change|F-change|sigfig=2}}—between the water surface and the air above.{{cite news|author=B. Geerts|year=1998|url=http://www-das.uwyo.edu/~geerts/cwx/notes/chap10/lake_effect_snow.html|title=Lake Effect Snow.|access-date=2008-12-24|publisher=University of Wyoming|archive-date=2020-11-06|archive-url=https://web.archive.org/web/20201106092611/http://www-das.uwyo.edu/~geerts/cwx/notes/chap10/lake_effect_snow.html|url-status=dead}} Because of this temperature difference, warmth and moisture are transported upward, condensing into vertically oriented clouds which produce snow showers. The temperature decrease with height and cloud depth are directly affected by both the water temperature and the large-scale environment. The stronger the temperature decrease with height, the taller the clouds get, and the greater the precipitation rate becomes.{{cite web|url=http://www.comet.ucar.edu/class/smfaculty/byrd/sld010.htm |publisher=University Corporation for Atmospheric Research |title=Lake Effect Snow |date=1998-06-03 |access-date=2009-07-12 |author=Greg Byrd |url-status=dead |archive-url=https://web.archive.org/web/20090617013142/http://www.comet.ucar.edu/class/smfaculty/byrd/sld010.htm |archive-date=2009-06-17}}

File:WorldwideTCpeaks.gif

File:Mean sst equatorial pacific.gif

{{Main|Tropical cyclogenesis|Tropical cyclones and climate change}}

Ocean temperature of at least 26.5°C (79.7°F) spanning through at minimum a 50-metre depth is one of the precursors needed to maintain a tropical cyclone (a type of mesocyclone).{{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}}{{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}} These warm waters are needed to maintain the warm core that fuels tropical systems. This value is well above 16.1 °C (60.9 °F), the long term global average surface temperature of the oceans.{{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}} 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 hPa level, or 5.9 km) can lead to tropical cyclogenesis at lower water temperatures, as a certain lapse rate is required to force the atmosphere to be unstable enough for convection. In a moist atmosphere, this lapse rate is 6.5 °C/km, while in an atmosphere with less than 100% relative humidity, the required lapse rate is 9.8 °C/km.{{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}}

At the 500 hPa level, the air temperature averages −7 °C (18 °F) within the tropics, but air in the tropics is normally dry at this height, giving the air room to wet-bulb, or cool as it moistens, to a more favorable temperature that can then support convection. A wet-bulb temperature at 500 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 °C in the sea surface temperature for each 1 °C change at 500 hpa.

Inside a cold cyclone, 500 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 hPa level, is normally a requirement for development. However, when dry air is found at the same height, temperatures at 500 hPa need to be even colder as dry atmospheres require a greater lapse rate for instability than moist atmospheres.{{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}}{{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}} At heights near the tropopause, the 30-year average temperature (as measured in the period encompassing 1961 through 1990) was −77 °C (−132 °F).{{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}} One example of a tropical cyclone maintaining itself over cooler waters was Epsilon late in the 2005 Atlantic hurricane season.{{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?}}

{{Portal|Oceans}}

• {{annotated link|El Niño–Southern Oscillation}}
• {{annotated link|Global surface temperature}}
• {{annotated link|Halocline}}
• {{annotated link|Instrumental temperature record}}
• {{annotated link|Marine heatwave}}
• {{annotated link|Ocean heat content}}
• {{annotated link|Pacific decadal oscillation}}
• {{annotated link|Sea level rise}}

{{Reflist|2}}

• [https://www.star.nesdis.noaa.gov/socd/ov/?tab=settings&zoom=4&cLat=33.8555&cLon=-71.5078&crs=EPSG4326&b_o_layers=2_0_5_FFFFF&s1L=T&s1I=3&s1P=0&s1O=0.78&s1S=T&s1Lg=T&s1Va=F&s2L=F&s2I=0&s2P=0&s2O=0.75&s2S=F&s2Lg=F&s2Va=F&s1s2Sp=F&vS=T&v1L=F&v2L=T&fS=F&f1L=F&f1Ln=1.00&f1Gd=0.010&f1Va=2.00&hS=F&hL=F&hLg=F&hW=25&hP=1010&eeS=F&eqL=F&eqMM=3.00&voL=F&wfL=F&tgS=T NOAA OceanView Blended SST and animated Surface Currents]
• [https://earth.nullschool.net/#current/ocean/surface/currents/overlay=sea_surface_temp/winkel3 Global map of current sea surface temperatures]
• [https://earth.nullschool.net/#current/ocean/surface/currents/overlay=sea_surface_temp_anomaly/winkel3 Global map of current sea surface temperature anomalies]
• [http://www.star.nesdis.noaa.gov/sod/sst/squam SQUAM] {{Webarchive|url=https://web.archive.org/web/20160306055154/http://www.star.nesdis.noaa.gov/sod/sst/squam/ |date=2016-03-06 }}, SST Quality Monitor (A near real-time Global QC Tool for monitoring time-series stability & cross-platform consistency of satellite SST)
• [http://www.star.nesdis.noaa.gov/sod/sst/iquam iQuam] {{Webarchive|url=https://web.archive.org/web/20180623110254/https://www.star.nesdis.noaa.gov/sod/sst/iquam/ |date=2018-06-23 }}, in situ SST Quality Monitor (A near real-time quality control & monitoring system for in situ SST measured by ships and buoys)
• [http://www.star.nesdis.noaa.gov/sod/sst/micros MICROS] {{Webarchive|url=https://web.archive.org/web/20160305102039/http://www.star.nesdis.noaa.gov/sod/sst/micros/ |date=2016-03-05 }}, Monitoring of IR Clear-sky Radiances over Oceans for SST

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