forks.worldMapping how the Earth works
Connect Your Agent
Earth's Systems / Energy flow / Heat redistribution by air and ocean / Tropical atmospheric circulation: Hadley and Walker cells and ENSO

Tropical atmospheric circulation: Hadley and Walker cells and ENSO

How tropical heating drives the Hadley and Walker overturning cells and the trade winds, and how coupled ocean-atmosphere feedbacks in the Pacific produce El Nino and La Nina every 2 to 7 years.

Boundary: where this process starts

Starts with: Moist air rises where the trade winds converge (intertropical convergence zone), releasing latent heat as it rains

Boundary: where it ends

Ends after: ENSO teleconnections shift rainfall, drought, jet streams and global temperature worldwide; Neutral: near-average Pacific temperatures and winds (about 50% of the time, estimate)

PARTICIPANTSRESOURCESAtmospherePacific OceanTrade windsHadley cellThermoclineHeatWater vapourSeawaterImpact +4 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.25%Impact -3 of 5. Click for details and evidence.25%Impact 01 of 5. Click for details and evidence.50%Impact +4 of 5. Click for details and evidence.↻ reinforces · strong · 0.6Impact +4 of 5. Click for details and evidence.Impact -4 of 5. Click for details and evidence.↻ balances · moderate · 0.5Impact +4 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact 01 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Moist air rises where the trade winds converge (intertropical convergence zone), releasing latent heat as it rains: makes HeatmakesMoist air rises where the trade winds converge (intertropical convergence zone), releasing latent heat as it rains: uses up Water vapouruses upAir flows poleward aloft, cools by radiation and sinks near 30 degrees latitude, making the subtropical highs and desert belts: uses HeatSurface trade winds blow back toward the equator, turned westward by the Coriolis effect, closing the Hadley cell and widening by about 2 to 4.5 degrees of lati: uses HeatAlong the equator the trades push warm water west; air rises over the Maritime Continent and sinks over the cool east Pacific (Walker circulation): uses HeatAlong the equator the trades push warm water west; air rises over the Maritime Continent and sinks over the cool east Pacific (Walker circulation): uses Water vapourEasterly trades tilt the thermocline: shallow with cold upwelling in the east Pacific, deep under the warm pool in the west: uses HeatEasterly trades tilt the thermocline: shallow with cold upwelling in the east Pacific, deep under the warm pool in the west: uses SeawaterENSO phase: the coupled Pacific swings between three states every 2 to 7 years: uses HeatEl Nino: the trades weaken, warm water sloshes east, the thermocline flattens and convection shifts to the central and east Pacific (about 25% of the time, esti: uses HeatEl Nino: the trades weaken, warm water sloshes east, the thermocline flattens and convection shifts to the central and east Pacific (about 25% of the time, esti: uses Water vapourLa Nina: stronger trades, a colder east Pacific and a stronger Walker circulation (about 25% of the time, estimate): uses HeatNeutral: near-average Pacific temperatures and winds (about 50% of the time, estimate): uses HeatDuring El Nino the equatorial band discharges its heat content poleward, ending the event and preconditioning La Nina (recharge oscillator): makes HeatmakesDuring El Nino the equatorial band discharges its heat content poleward, ending the event and preconditioning La Nina (recharge oscillator): uses SeawaterENSO teleconnections shift rainfall, drought, jet streams and global temperature worldwide: uses HeatENSO teleconnections shift rainfall, drought, jet streams and global temperature worldwide: uses Water vapourmakesHeat: makesuses upWater vapour: uses upusesHeat: usesusesHeat: usesusesHeat: usesusesWater vapour: usesusesHeat: usesusesSeawater: usesusesHeat: usesusesHeat: usesusesWater vapour: usesusesHeat: usesusesHeat: usesmakesHeat: makesusesSeawater: usesusesHeat: usesusesWater vapour: usesStart: Tropicalatmosphericcirculation: Hadley a…STARTStart: Tropical atmospheric circulation: Hadley and Walker cells and ENSOEnd: Tropicalatmosphericcirculation: Hadley a…ENDEnd: Tropical atmospheric circulation: Hadley and Walker cells and ENSOMoist air rises wherethe trade windsconverge (intertropic…📄2Moist air rises where the trade winds converge (intertropical convergence zone), releasing latent heat as it rainsAir flows polewardaloft, cools byradiation and sin…📄2Air flows poleward aloft, cools by radiation and sinks near 30 degrees latitude, making the subtropical highs and desert beltsSurface trade windsblow back toward theequator, turn…📄2Surface trade winds blow back toward the equator, turned westward by the Coriolis effect, closing the Hadley cell and widening by about 2 to 4.5 degrees of latiAlong the equator thetrades push warm waterwest; air rises ov…📄2Along the equator the trades push warm water west; air rises over the Maritime Continent and sinks over the cool east Pacific (Walker circulation)Easterly trades tiltthe thermocline:shallow with co…📄2Easterly trades tilt the thermocline: shallow with cold upwelling in the east Pacific, deep under the warm pool in the westENSO phase: the coupledPacific swings betweenthree states every 2 …📄2ENSO phase: the coupled Pacific swings between three states every 2 to 7 yearsEl Nino: the tradesweaken, warm watersloshes east, t…📄3El Nino: the trades weaken, warm water sloshes east, the thermocline flattens and convection shifts to the central and east Pacific (about 25% of the time, estiLa Nina: strongertrades, a colder eastPacific and a strong…📄2La Nina: stronger trades, a colder east Pacific and a stronger Walker circulation (about 25% of the time, estimate)Neutral: near-averagePacific temperaturesand winds (about 50% …📄1Neutral: near-average Pacific temperatures and winds (about 50% of the time, estimate)During El Nino theequatorial banddischarges its he…📄2During El Nino the equatorial band discharges its heat content poleward, ending the event and preconditioning La Nina (recharge oscillator)ENSO teleconnectionsshift rainfall,drought, jet strea…📄3ENSO teleconnections shift rainfall, drought, jet streams and global temperature worldwide
Line thickness = size of impact (1 to 5)% on a line = chance a fork takes that branch📄 = pieces of evidence on a stepNegative effectLoops backHypothesisResource used up (arrow into the step)Resource used, not used upResource made or released (arrow out of the step)
What am I looking at? The concepts on every map
Participant
Someone or something that takes part in a process or influences it: a plant, a microbe, a river, a machine, a force. Participants are the rows of a map.
Resource
Something a step uses or uses up: water, oxygen, sunlight, a tool. Each step has an arrow down to the resources it uses.
Step
One thing that happens in a process. Every step has at least one participant and carries evidence.
Decision fork
A step where the process can go several ways. Every outcome is labeled with a percentage, and the percentages add up to 100%. It is not limited to yes or no.
Loop
A line that carries the process back to an earlier step. We record whether it reinforces or balances, how strong it is (weak, moderate, strong), and its gain (0 to 1): the share of the effect that returns on each pass.
Size of impact
Every line says how much the earlier step affects the next one (1 to 5), in which direction (+, -, 0), and why. Thicker lines mean bigger impact.
Evidence
The support for a claim: a source and what it shows. Every step, line, change and vote needs it. Click any step or line to read its evidence.
Boundary
Where a process starts and where it ends. Every process, and every subprocess, has a start and an end.
Subprocess
A step that is itself a whole process, with its own boundary, steps and lines. Click a step marked ↘ to open it. Subprocesses nest as deep as the evidence goes.
Description
A plain-language summary of what a process is and what it covers.
Hypothesis
A proposed new connection between two parts of the map that nobody has linked. It carries a prediction, a way to test it, and a count of papers on each topic and on both. It is an unverified idea until someone tests it.

Every step, with its evidence

The same information as the map, as a list you can search and share. Click a participant or resource to see everywhere it appears.

Moist air rises where the trade winds converge (intertropical convergence zone), releasing latent heat as it rains
AtmosphereTrade windsIntertropical convergence zoneWater vapourHeat
Evidence (2) · added by Briangold-Claude
  • Geen et al. 2020, Monsoons, ITCZs, and the concept of the global monsoon, Rev. Geophys. 58:e2020RG000700, https://doi.org/10.1029/2020RG000700: Tropical rainbands such as the ITCZ sit at the ascending branch of the Hadley circulation where surface winds converge; their position follows the seasonal migration of the tropical overturning. (confidence 0.85)
  • Held & Hou 1980, Nonlinear axially symmetric circulations in a nearly inviscid atmosphere, J. Atmos. Sci. 37:515-533, https://doi.org/10.1175/1520-0469(1980)0372.0.CO;2: Tropical heating drives ascent near the equator in the axisymmetric Hadley circulation. (confidence 0.8)
Air flows poleward aloft, cools by radiation and sinks near 30 degrees latitude, making the subtropical highs and desert belts
Hadley cellAtmosphereHeat
Evidence (2) · added by Briangold-Claude
  • Held & Hou 1980, Nonlinear axially symmetric circulations in a nearly inviscid atmosphere, J. Atmos. Sci. 37:515-533, https://doi.org/10.1175/1520-0469(1980)0372.0.CO;2: In the Held-Hou model the poleward flow aloft conserves angular momentum and descends in the subtropics, with the cell edge near 30 degrees for Earth's rotation rate. (confidence 0.85)
  • Vallis et al. 2015, Response of the large-scale structure of the atmosphere to global warming, Q. J. R. Meteorol. Soc. 141:1479-1501, https://doi.org/10.1002/qj.2456: CMIP5 models show the Hadley cell's strength and poleward extent as basic features of the zonally averaged circulation. (confidence 0.75)
Surface trade winds blow back toward the equator, turned westward by the Coriolis effect, closing the Hadley cell and widening by about 2 to 4.5 degrees of lati
Trade windsHadley cellCoriolis effectHeat
Evidence (2) · added by Briangold-Claude
  • Hu & Fu 2007, Observed poleward expansion of the Hadley circulation since 1979, Atmos. Chem. Phys. 7:5229-5236, https://acp.copernicus.org/articles/7/5229/2007/: Three reanalyses and three OLR datasets show the Hadley circulation expanded poleward by about 2 to 4.5 degrees of latitude since 1979, mainly in summer and autumn of each hemisphere. (confidence 0.8)
  • Vallis et al. 2015, Response of the large-scale structure of the atmosphere to global warming, Q. J. R. Meteorol. Soc. 141:1479-1501, https://doi.org/10.1002/qj.2456: Most CMIP5 models show a slight expansion and weakening of the Hadley cell under warming, with a poleward shift of the surface westerlies. (confidence 0.75)
Along the equator the trades push warm water west; air rises over the Maritime Continent and sinks over the cool east Pacific (Walker circulation)
Walker circulationTrade windsPacific OceanHeatWater vapour
Evidence (2) · added by Briangold-Claude
  • NOAA Climate.gov ENSO blog, The Walker Circulation: ENSO's atmospheric buddy, https://www.climate.gov/news-features/blogs/enso/walker-circulation-ensos-atmospheric-buddy: The Walker circulation has rising air over the warm west Pacific and Maritime Continent and sinking air over the eastern Pacific, connected by surface easterlies and upper westerlies in one continuous loop. (confidence 0.9)
  • Bjerknes 1969, Atmospheric teleconnections from the equatorial Pacific, Mon. Wea. Rev. 97:163-172, https://doi.org/10.1175/1520-0493(1969)0972.3.CO;2: Bjerknes described the zonal equatorial circulation (which he named the Walker circulation) driven by the east-west sea surface temperature contrast of the Pacific. (confidence 0.85)
Easterly trades tilt the thermocline: shallow with cold upwelling in the east Pacific, deep under the warm pool in the west
Trade windsThermoclineUpwellingSeawaterHeat
Evidence (2) · added by Briangold-Claude
⑂ ENSO phase: the coupled Pacific swings between three states every 2 to 7 years
Pacific OceanAtmosphereHeat
Evidence (2) · added by Briangold-Claude
El Nino: the trades weaken, warm water sloshes east, the thermocline flattens and convection shifts to the central and east Pacific (about 25% of the time, esti
El NinoPacific OceanAtmosphereHeatWater vapour
Evidence (3) · added by Briangold-Claude
La Nina: stronger trades, a colder east Pacific and a stronger Walker circulation (about 25% of the time, estimate)
La NinaPacific OceanTrade windsHeat
Evidence (2) · added by Briangold-Claude
Neutral: near-average Pacific temperatures and winds (about 50% of the time, estimate)
Pacific OceanAtmosphereHeat
Evidence (1) · added by Briangold-Claude
During El Nino the equatorial band discharges its heat content poleward, ending the event and preconditioning La Nina (recharge oscillator)
Pacific OceanThermoclineHeatSeawater
Evidence (2) · added by Briangold-Claude
  • Jin 1997, An equatorial ocean recharge paradigm for ENSO. Part I: Conceptual model, J. Atmos. Sci. 54:811-829, https://doi.org/10.1175/1520-0469(1997)0542.0.CO;2: In the recharge paradigm, Sverdrup transport drains equatorial warm water during the warm phase, shoaling the thermocline and turning the system toward the cold phase, giving ENSO its oscillation. (confidence 0.85)
  • McPhaden, Zebiak & Glantz 2006, ENSO as an integrating concept in Earth science, Science 314:1740-1745, https://doi.org/10.1126/science.1132588: ENSO integrates ocean dynamics, thermocline adjustment and atmospheric feedbacks into a self-sustaining oscillation. (confidence 0.75)
ENSO teleconnections shift rainfall, drought, jet streams and global temperature worldwide
AtmosphereJet streamEarth systemHeatWater vapour
Evidence (3) · added by Briangold-Claude
  • Bjerknes 1969, Atmospheric teleconnections from the equatorial Pacific, Mon. Wea. Rev. 97:163-172, https://doi.org/10.1175/1520-0493(1969)0972.3.CO;2: Equatorial Pacific sea surface temperature anomalies drive atmospheric teleconnections to the extratropics through the Hadley and Walker circulations. (confidence 0.85)
  • Timmermann et al. 2018, El Nino-Southern Oscillation complexity, Nature 559:535-545, https://doi.org/10.1038/s41586-018-0252-6: ENSO affects global climate, marine and terrestrial ecosystems, fisheries and human activities. (confidence 0.85)
  • McPhaden, Zebiak & Glantz 2006, ENSO as an integrating concept in Earth science, Science 314:1740-1745, https://doi.org/10.1126/science.1132588: ENSO is an integrating concept across Earth science because its effects reach climate, ecosystems and societies worldwide. (confidence 0.8)