
Sea surface temperature (or ocean surface temperature) is the
temperature of ocean water close to the surface. The exact meaning of ''surface'' varies in the literature and in practice. It is usually between and below the
sea
A sea is a large body of salt water. There are particular seas and the sea. The sea commonly refers to the ocean, the interconnected body of seawaters that spans most of Earth. Particular seas are either marginal seas, second-order section ...
surface. Sea surface temperatures greatly modify
air mass
In meteorology, an air mass is a volume of air defined by its temperature and humidity. Air masses cover many hundreds or thousands of square miles, and adapt to the characteristics of the surface below them. They are classified according to ...
es in the
Earth's atmosphere
The atmosphere of Earth is composed of a layer of gas mixture that surrounds the Earth's planetary surface (both lands and oceans), known collectively as air, with variable quantities of suspended aerosols and particulates (which create weathe ...
within a short distance of the shore. The
thermohaline circulation
Thermohaline circulation (THC) is a part of the large-scale Ocean current, ocean circulation driven by global density gradients formed by surface heat and freshwater fluxes. The name ''thermohaline'' is derived from ''wikt:thermo-, thermo-'', r ...
has a major impact on average sea surface temperature throughout most of the world's oceans.
Warm sea surface temperatures can develop and
strengthen cyclones over the ocean. Tropical cyclones can also cause a cool wake. This is due to turbulent mixing of the upper of the ocean. Sea surface temperature changes during the day. This is like the air above it, but to a lesser degree. There is less variation in sea surface temperature on breezy days than on calm days.
Coastal sea surface temperatures can cause offshore winds to generate
upwelling
Upwelling is an physical oceanography, oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted sur ...
, which can significantly cool or warm nearby landmasses, but shallower waters over a
continental shelf
A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an islan ...
are often warmer. Onshore winds can cause a considerable warm-up even in areas where upwelling is fairly constant, such as the northwest coast of
South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...
. Coastal sea surface temperature values are important within
numerical weather prediction
Numerical weather prediction (NWP) uses mathematical models of the atmosphere and oceans to weather forecasting, predict the weather based on current weather conditions. Though first attempted in the 1920s, it was not until the advent of comput ...
as the sea surface temperature influences the atmosphere above, such as in the formation of
sea breeze
A sea breeze or onshore breeze is a wind that blows in the afternoon from a large body of water toward or onto a landmass. By contrast, a land breeze or offshore breeze is a wind that blows in the night from a landmass toward or onto a large ...
s and
sea fog.
It is very likely that global mean sea surface temperature increased by 0.88 °C between 1850–1900 and 2011–2020 due to
global warming
Present-day climate change includes both global warming—the ongoing increase in global average temperature—and its wider effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes ...
, with most of that warming (0.60 °C) occurring between 1980 and 2020.
[Fox-Kemper, B., H.T. Hewitt, C. Xiao, G. Aðalgeirsdóttir, S.S. Drijfhout, T.L. Edwards, N.R. Golledge, M. Hemer, R.E. Kopp, G. Krinner, A. Mix, D. Notz, S. Nowicki, I.S. Nurhati, L. Ruiz, J.-B. Sallée, A.B.A. Slangen, and Y. Yu, 2021]
Chapter 9: Ocean, Cryosphere and Sea Level Change
I
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, New York, USA, pages 1211–1362, doi:10.1017/9781009157896.011. The temperatures over land are rising faster than Ocean temperature, ocean temperatures. This is because the
Ocean heat content, ocean absorbs about 90% of
excess heat generated by
climate change
Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...
.
Definitions

Sea surface temperature (SST), or ocean surface temperature, is the water
temperature
Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...
close to the
ocean
The ocean is the body of salt water that covers approximately 70.8% of Earth. The ocean is conventionally divided into large bodies of water, which are also referred to as ''oceans'' (the Pacific, Atlantic, Indian Ocean, Indian, Southern Ocean ...
's surface. The exact meaning of ''surface'' varies according to the measurement method used, but it is between and below the
sea
A sea is a large body of salt water. There are particular seas and the sea. The sea commonly refers to the ocean, the interconnected body of seawaters that spans most of Earth. Particular seas are either marginal seas, second-order section ...
surface.
For comparison, the
sea surface skin temperature relates to the top 20 or so
micrometres
The micrometre (English in the Commonwealth of Nations, Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a uni ...
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."
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
Ocean heat content (OHC) or ocean heat uptake (OHU) is the energy absorbed and stored by oceans, and is thus an important indicator of global warming. Ocean heat content is calculated by measuring ocean temperature at many different locations and ...
and
ocean stratification
Ocean stratification is the natural separation of an ocean's water into horizontal layers by Density of water, density. This is generally stable stratification, because warm water floats on top of cold water, and heating is mostly from the sun, whi ...
.
The increase of both ocean surface temperature and deeper ocean temperature is an important
effect of climate change on oceans.
Extent of "surface"
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
Pole or poles may refer to:
People
*Poles (people), another term for Polish people, from the country of Poland
* Pole (surname), including a list of people with the name
* Pole (musician) (Stefan Betke, born 1967), German electronic music artist
...
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.
Variations and changes
Local variations
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
Thermal inertia is a term commonly used to describe the observed delays in a body's temperature response during heat transfers. The phenomenon exists because of a body's ability to both store and transport heat relative to its environment. Sinc ...
. On calm days, the temperature can vary by .
The temperature of the ocean at depth lags the Earth's atmosphere temperature by 15 days per , which means for locations like the
Aral Sea
The Aral Sea () was an endorheic lake lying between Kazakhstan to its north and Uzbekistan to its south, which began shrinking in the 1960s and had largely dried up into desert by the 2010s. It was in the Aktobe and Kyzylorda regions of Kazakhst ...
, temperatures near its bottom reach a maximum in December and a minimum in May and June. 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
Ekman transport is part of Ekman motion theory, first investigated in 1902 by Vagn Walfrid Ekman. Winds are the main source of energy for ocean circulation, and Ekman transport is a component of wind-driven ocean current. Ekman transport occurs w ...
. 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. Offshore of
river delta
A river delta is a landform, archetypically triangular, created by the deposition of the sediments that are carried by the waters of a river, where the river merges with a body of slow-moving water or with a body of stagnant water. The creat ...
s, freshwater flows over the top of the denser seawater, which allows it to heat faster due to limited vertical mixing. Remotely sensed SST can be used to detect the surface temperature signature due to
tropical cyclone
A tropical cyclone is a rapidly rotating storm system with a low-pressure area, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its locat ...
s. 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.
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). Other sources of short-term SST fluctuation include
extratropical cyclone
Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are low-pressure areas which, along with the anticyclones of high-pressure areas, drive the weather over much of the Earth. Extratropical cyclones are capable of p ...
s, rapid influxes of
glacial
A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
fresh water and concentrated
phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater Aquatic ecosystem, ecosystems. The name comes from the Greek language, Greek words (), meaning 'plant', and (), mea ...
blooms due to seasonal cycles or agricultural run-off.
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.
Atlantic Multidecadal Oscillation
Ocean current
An ocean current is a continuous, directed movement of seawater generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, cabbeling, and temperature and salinity differences. Depth contours, sh ...
s, such as the
Atlantic Multidecadal Oscillation
The Atlantic Multidecadal Oscillation (AMO), also known as Atlantic Multidecadal Variability (AMV), is the theorized variability of the sea surface temperature (SST) of the North Atlantic Ocean on the timescale of several decades.
While there ...
, can affect sea surface temperatures over several decades. 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. Atmospheric internal variability, changes in ocean circulation, or anthropogenic drivers may control the multidecadal temperature variability associated with AMO. These changes in North Atlantic SST may influence winds in the subtropical North Pacific and produce warmer SSTs in the western Pacific Ocean.
Regional variations
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. 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".
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
The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or approximately 20% of the water area of Earth#Surface, Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia (continent), ...
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
The Humboldt Current, also called the Peru Current, is a cold, low-salinity ocean current that flows north along the western coast of South America.Montecino, Vivian, and Carina B. Lange. "The Humboldt Current System: Ecosystem components and pro ...
. When El Niño conditions last for many months, extensive
ocean warming
Ocean heat content (OHC) or ocean heat uptake (OHU) is the energy absorbed and stored by oceans, and is thus an important indicator of Climate change, global warming. Ocean heat content is calculated by measuring ocean temperature at many differe ...
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.
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.
Recent increase due to climate change
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 0.06K per decade during 1985–89 to 0.27K 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.]
Measurement
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
A thermocline (also known as the thermal layer or the metalimnion in lakes) is
a distinct layer based on temperature within a large body of fluid (e.g. water, as in an ocean or lake; or air, e.g. an atmosphere) with a high gradient of distinct te ...
). Sea surface temperature measurements are confined to the top portion of the ocean, known as the near-surface layer.
Thermometers
The sea surface temperature was one of the first oceanographic variables to be measured. Benjamin Franklin
Benjamin Franklin (April 17, 1790) was an American polymath: a writer, scientist, inventor, statesman, diplomat, printer, publisher and Political philosophy, political philosopher.#britannica, Encyclopædia Britannica, Wood, 2021 Among the m ...
suspended a mercury thermometer
Mercury most commonly refers to:
* Mercury (planet), the closest planet to the Sun
* Mercury (element), a chemical element
* Mercury (mythology), a Roman deity
Mercury or The Mercury may also refer to:
Companies
* Mercury (toy manufacturer) ...
from a ship while travelling between the United States and Europe in his survey of the Gulf Stream
The Gulf Stream is a warm and swift Atlantic ocean current that originates in the Gulf of Mexico and flows through the Straits of Florida and up the eastern coastline of the United States, then veers east near 36°N latitude (North Carolin ...
in the late eighteenth century. SST was later measured by dipping a thermometer
A thermometer is a device that measures temperature (the hotness or coldness of an object) or temperature gradient (the rates of change of temperature in space). A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb ...
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 due to the heat of the engine room.
Fixed weather buoy
Weather buoys are instruments which collect weather and ocean data within the world's oceans, as well as aid during emergency response to chemical spills, legal proceedings, and engineering design. Moored buoys have been in use since 1951, whil ...
s measure the water temperature at a depth of . 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.
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. A large network of coastal buoys in U.S. waters is maintained by the National Data Buoy Center
The National Data Buoy Center (NDBC) is a part of the National Oceanic and Atmospheric Administration's (NOAA) National Weather Service (NWS). NDBC designs, develops, operates, and maintains a network of data collecting buoys and coastal stations ...
(NDBC). 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
EL, El or el may refer to:
Arts and entertainment Fictional entities
* El, a character from the manga series ''Shugo Chara!'' by Peach-Pit
* Eleven (''Stranger Things'') (El), a fictional character in the TV series ''Stranger Things''
* El, fami ...
phenomenon.
Weather satellites
Weather satellites have been available to determine sea surface temperature information since 1967, with the first global composites created during 1970. Since 1982, satellite
A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scient ...
s 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
is a Latin phrase meaning 'in place' or 'on site', derived from ' ('in') and ' ( ablative of ''situs'', ). The term typically refers to the examination or occurrence of a process within its original context, without relocation. The term is use ...
temperature measurements. The satellite measurement is made by sensing the ocean radiation
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or a material medium. This includes:
* ''electromagnetic radiation'' consisting of photons, such as radio waves, microwaves, infr ...
in two or more wavelengths within the infrared
Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...
part of the electromagnetic spectrum
The electromagnetic spectrum is the full range of electromagnetic radiation, organized by frequency or wavelength. The spectrum is divided into separate bands, with different names for the electromagnetic waves within each band. From low to high ...
or other parts of the spectrum which can then be empirically related to SST. These wavelengths are chosen because they are:
# within the peak of the blackbody radiation
Black-body radiation is the thermal electromagnetic radiation within, or surrounding, a body in thermodynamic equilibrium with its environment, emitted by a black body (an idealized opaque, non-reflective body). It has a specific continuous spectr ...
expected from the Earth, and
# able to transmit adequately well through the atmosphere
An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...
The satellite-measured SST provides both a synoptic view of the ocean and a high frequency of repeat views, allowing the examination of basin-wide upper ocean
The ocean is the body of salt water that covers approximately 70.8% of Earth. The ocean is conventionally divided into large bodies of water, which are also referred to as ''oceans'' (the Pacific, Atlantic, Indian Ocean, Indian, Southern Ocean ...
dynamics not possible with ships or buoys. NASA's
/span> (National Aeronautic and Space Administration) Moderate Resolution Imaging Spectroradiometer (MODIS)
/span> SST satellites have been providing global SST data since 2000, available with a one-day lag. NOAA's GOES (Geostationary Orbiting Earth Satellites)
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 In thermofluids dynamics, the bulk temperature, or the average bulk temperature in the thermal fluid, is a convenient reference point for evaluating properties related to convective heat transfer, particularly in applications related to flow in pi ...
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. 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 satellite
A weather satellite or meteorological satellite is a type of Earth observation satellite that is primarily used to monitor the weather and climate of the Earth. Satellites are mainly of two types: polar orbiting (covering the entire Earth asyn ...
s, which peak just above the ocean's surface, knowledge of the sea surface temperature is important to their calibration.
Importance to the Earth's atmosphere
Sea surface temperature affects the behavior of the Earth's atmosphere
The atmosphere of Earth is composed of a layer of gas mixture that surrounds the Earth's planetary surface (both lands and oceans), known collectively as air, with variable quantities of suspended aerosols and particulates (which create weathe ...
above, so their initialization into atmospheric model
In atmospheric science, an atmospheric model is a mathematical model constructed around the full set of primitive equations, primitive, Dynamical systems theory, dynamical equations which govern atmospheric motions. It can supplement these equati ...
s is important. While sea surface temperature is important for tropical cyclogenesis
Tropical cyclogenesis is the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropics, tropical cyclogenesis occur are distinctly different from those through which temperate cyclogenesis occu ...
, it is also important in determining the formation of sea fog and sea breezes. Heat from underlying warmer waters can significantly modify an air mass over distances as short as to . For example, southwest of Northern Hemisphere extratropical cyclone
Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are low-pressure areas which, along with the anticyclones of high-pressure areas, drive the weather over much of the Earth. Extratropical cyclones are capable of p ...
s, curved cyclonic flow bringing cold air across relatively warm water bodies can lead to narrow lake-effect snow
Lake-effect snow is produced during cooler atmospheric conditions when a cold air mass moves across long expanses of warmer lake water. The lower layer of air, heated by the lake water, picks up water vapor from the lake and rises through colde ...
(or sea effect) bands. Those bands bring strong localized precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...
, often in the form of snow
Snow consists of individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes.
It consists of frozen crystalline water througho ...
, since large water bodies such as lakes efficiently store heat that results in significant temperature differences—larger than —between the water surface and the air above. 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.
Tropical cyclones
Ocean temperature of at least 26.5°C
The degree Celsius is the unit of temperature on the Celsius temperature scale "Celsius temperature scale, also called centigrade temperature scale, scale based on 0 ° for the melting point of water and 100 ° for the boiling point ...
(79.7°F
The Fahrenheit scale () is a temperature scale based on one proposed in 1724 by the German-Polish physicist Daniel Gabriel Fahrenheit (1686–1736). It uses the degree Fahrenheit (symbol: °F) as the unit. Several accounts of how he original ...
) spanning through at minimum a 50-metre
The metre (or meter in US spelling; symbol: m) is the base unit of length in the International System of Units (SI). Since 2019, the metre has been defined as the length of the path travelled by light in vacuum during a time interval of of ...
depth is one of the precursors needed to maintain a tropical cyclone
A tropical cyclone is a rapidly rotating storm system with a low-pressure area, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its locat ...
(a type of mesocyclone
A mesocyclone is a meso-gamma mesoscale (or storm scale) region of rotation ( vortex), typically around in diameter, most often noticed on radar within thunderstorms. In the Northern Hemisphere, it is usually located in the right rear flank ( ...
). 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. 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
The pascal (symbol: Pa) is the unit of pressure in the International System of Units (SI). It is also used to quantify internal pressure, stress, Young's modulus, and ultimate tensile strength. The unit, named after Blaise Pascal, is an S ...
level, or 5.9 km) can lead to tropical cyclogenesis at lower water temperatures, as a certain lapse rate
The lapse rate is the rate at which an atmospheric variable, normally temperature in Earth's atmosphere, falls with altitude. ''Lapse rate'' arises from the word ''lapse'' (in its "becoming less" sense, not its "interruption" sense). In dry air, ...
is required to force the atmosphere to be unstable
In dynamical systems instability means that some of the outputs or internal state (controls), states increase with time, without bounds. Not all systems that are not Stability theory, stable are unstable; systems can also be marginal stability ...
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
Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation (meteorology), precipitation, dew, or fog t ...
, the required lapse rate is 9.8 °C/km.
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
The wet-bulb temperature is the lowest temperature that can be reached under current ambient conditions by the evaporation of water only. It is defined as the temperature of a parcel of air cooled to saturation (100% relative humidity) by the ...
at 500 hPa in a tropical atmosphere of is required to initiate convection if the water temperature is , 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 , which can initiate convection even in the driest atmospheres. This also explains why moisture in the mid-levels of the troposphere
The troposphere is the lowest layer of the atmosphere of Earth. It contains 80% of the total mass of the Atmosphere, planetary atmosphere and 99% of the total mass of water vapor and aerosols, and is where most weather phenomena occur. From the ...
, 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. At heights near the tropopause
The tropopause is the atmospheric boundary that demarcates the lowest two layers of the atmosphere of Earth – the troposphere and stratosphere – which occurs approximately above the equatorial regions, and approximately above the polar regi ...
, the 30-year average temperature (as measured in the period encompassing 1961 through 1990) was −77 °C (−132 °F). One example of a tropical cyclone
A tropical cyclone is a rapidly rotating storm system with a low-pressure area, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its locat ...
maintaining itself over cooler waters was Epsilon
Epsilon (, ; uppercase , lowercase or ; ) is the fifth letter of the Greek alphabet, corresponding phonetically to a mid front unrounded vowel or . In the system of Greek numerals it also has the value five. It was derived from the Phoenic ...
late in the 2005 Atlantic hurricane season
The 2005 Atlantic hurricane season was a record-breaking, devastating and deadly Atlantic hurricane season. It is the second-costliest hurricane season, just behind the 2017 season And 2024. It featured 28 tropical and subtropical storms, ...
.
See also
*
*
*
*
*
*
*
*
References
External links
NOAA OceanView Blended SST and animated Surface Currents
Global map of current sea surface temperatures
Global map of current sea surface temperature anomalies
SQUAM
, SST Quality Monitor (A near real-time Global QC Tool for monitoring time-series stability & cross-platform consistency of satellite SST)
iQuam
, in situ SST Quality Monitor (A near real-time quality control & monitoring system for in situ SST measured by ships and buoys)
MICROS
, Monitoring of IR Clear-sky Radiances over Oceans for SST
{{DEFAULTSORT:Sea Surface Temperature
Aquatic ecology
Meteorological phenomena
Marine meteorology
Oceanography
Thermodynamic cycles
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