el niño / southern oscillation (enso)

El El NiñoNiño / Southern / Southern OscillationOscillation(ENSO)(ENSO)

By Sagar BoraBy Sagar Bora

University of BremenUniversity of Bremen

04/19/23 2Presented by Sagar Bora

OutlineOutline

Motivation/HistoryMotivation/History El – NiEl – Niñño/La Nio/La Niñña definitiona definition Normal Conditions in the Pacific OceanNormal Conditions in the Pacific Ocean El – NiEl – Niñño Conditionso Conditions La-NiLa-Niñña Conditionsa Conditions Effects of El – NiEffects of El – Niñño and La-Nio and La-Niññaa El – NiEl – Niñño factso facts SummarySummary


El Niño El Niño

From the mid 18th century, Peruvian fisherman noticed that their harvest completely failed every few years.

This periodic event was associated with unusually warm waters off the coast of Peru.

Since the periodic warming almost always occurred around December, the fisherman named it El Niño, in reference to the Christ child.

MotivatioMotivationn

DefinitionsDefinitions Normal Normal conditionsconditions

El NinoEl Nino La La NinaNina

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FactsFacts SummarSummaryy


Southern OscillationSouthern Oscillation

In the late 19th century Gilbert Walker, the head of the Indian Meteorological Service notices that the Indian monsoon fails periodically every few years, leading to drought and famine in India.

Search for a way to predict the Indian monsoon.

Identified a peculiar see-saw relationship between pressure over the maritime continent and India and the Pacific near South America.

He called this relationship the Southern Oscillation.




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ENSOENSO

In 1969, UCLA professor Jacob Bjerknes was the first to recognize that El Niño and the Southern Oscillation are actually manifestations of the same physical phenomenon and that it results from an unstable interaction between the atmosphere and the ocean. This resulted in the term ENSO to refer to this phenomenon.




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Why should we study El Niño?Why should we study El Niño?

Reduced upwelling off the coast of South Reduced upwelling off the coast of South America. So periodic failure of fishery America. So periodic failure of fishery near Peru, which normally is responsible near Peru, which normally is responsible for one-fifth of global fish production. for one-fifth of global fish production. High coral mortalityHigh coral mortality

Drought in South-east Asia, India, Drought in South-east Asia, India, Australia and AfricaAustralia and Africa

Heavy rainfall in the South AmericasHeavy rainfall in the South Americas




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El – Niño definitionEl – Niño definition

From: www.weathersa.co.za El NiñoNiño : When the When the three-month running mean three-month running mean of of

the the Sea Surface Temperature Sea Surface Temperature anomalies in the anomalies in the Nino 3.4 region are greater than or equal to 0.5°C, Nino 3.4 region are greater than or equal to 0.5°C, an El Niño event is assumed to be taking place. an El Niño event is assumed to be taking place.




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La Niña definitionLa Niña definition

From: www.weathersa.co.za La NiñaNiña : When the When the three-month running mean three-month running mean

of the of the Sea Surface Temperature Sea Surface Temperature anomalies in anomalies in the Nino 3.4 region are greater than or equal the Nino 3.4 region are greater than or equal to -0.5°C, an La Nina event is assumed to be to -0.5°C, an La Nina event is assumed to be taking place. taking place.




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Normal Conditions in the Normal Conditions in the Pacific OceanPacific Ocean

Nutrient rich cool water Nutrient rich cool water along the Peruvian along the Peruvian coast (eastern pacific) coast (eastern pacific) due to upwelling;due to upwelling;

good for marine life;good for marine life; Shallow mixed layer; Shallow mixed layer;

thermocline raisedthermocline raised 3 to 8 °C warmer water 3 to 8 °C warmer water

in the west Pacific near in the west Pacific near Australia, IndonesiaAustralia, Indonesia

Deep mixed layer; Deep mixed layer; thermocline pushed thermocline pushed down down

From: www.weathersa.co.za




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Normal Conditions in the Normal Conditions in the Pacific OceanPacific Ocean




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Source: http://www.wrh.noaa.gov/fgz/science/elnino.php?wfo=fgz


Normal Conditions in the Normal Conditions in the atmosphereatmosphere

High pressure in the east above High pressure in the east above the cold water, low pressure in the cold water, low pressure in the west above the warmer the west above the warmer waterwater

Pressure gradients result in Pressure gradients result in easterly trade winds which in easterly trade winds which in turn results in upwelling along turn results in upwelling along the Peruvian coastthe Peruvian coast

Trade winds brings moist warm Trade winds brings moist warm air towards Indonesian region air towards Indonesian region which rises and travels eastward which rises and travels eastward before sinking in the east. This before sinking in the east. This is a thermally direct circulation is a thermally direct circulation found by Sir G. Walker. found by Sir G. Walker.





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El – Niño Conditions in the El – Niño Conditions in the atmosphere atmosphere

Easterly winds weakens, even Easterly winds weakens, even changes directions sometimes changes directions sometimes and becomes westerlies due to and becomes westerlies due to change in the sign of pressure change in the sign of pressure gradient. Sir Walker called gradient. Sir Walker called this east-west seesaw in this east-west seesaw in

southern Pacific pressuresouthern Pacific pressure ““Southern OscillationSouthern Oscillation””





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El Niño conditions in the El Niño conditions in the Pacific OceanPacific Ocean

Due to change in the wind Due to change in the wind direction, the currents on the direction, the currents on the ocean also slows down or ocean also slows down or changes direction from changes direction from westward to eastward. westward to eastward.

SST rises in the eastern SST rises in the eastern pacific and the western pacific and the western pacific cools down a bit; pacific cools down a bit; Downwelling occurs off the Downwelling occurs off the coast of Peru; nutrient-less coast of Peru; nutrient-less warm surface water leads to warm surface water leads to decline in marine lifedecline in marine life

Rainy conditions move with Rainy conditions move with the warmer SST and dry the warmer SST and dry conditions move with the conditions move with the coldcoldFrom:

www.weathersa.co.za




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El Niño Conditions in the El Niño Conditions in the Pacific OceanPacific Ocean




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A normal year and an El Niño A normal year and an El Niño yearyear





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La Niña conditionsLa Niña conditions During La Niña years, the During La Niña years, the

upwelling off the Peruvian upwelling off the Peruvian coast is enhanced and the coast is enhanced and the SSTs in the SSTs in the Nino regions Nino regions become cooler than usual. become cooler than usual.

The Walker Circulation The Walker Circulation operates in the same way as operates in the same way as described for normal years, described for normal years, but because of the larger but because of the larger area of colder water off the area of colder water off the South American coast and South American coast and the displacement of warmer the displacement of warmer water to the west, the water to the west, the atmospheric pattern also atmospheric pattern also shifts accordingly. Heavier shifts accordingly. Heavier rainfall over Australia and rainfall over Australia and Indonesia and dry spans over Indonesia and dry spans over South AmericasSouth Americas

From: http://www.wrh.noaa.gov/




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La Niña conditions in the La Niña conditions in the Pacific OceanPacific Ocean




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Global impacts of El Niño Global impacts of El Niño




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Global impacts of La NiñaGlobal impacts of La Niña




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El Niño factsEl Niño facts

ENSO is not a weather anomaly, it’s a part ENSO is not a weather anomaly, it’s a part of a cycle. of a cycle.

Every weather anomaly throughout the Every weather anomaly throughout the world that occurs during an El Niño year is world that occurs during an El Niño year is not caused by that El Niño.not caused by that El Niño.

The impact of global warming on El Niño is not as yet known, speculation notwithstanding.

Forecasting El Niño’s onset does not tell us much about its other characteristics (e.g., intensity, frequency, duration).




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Summary and conclusionsSummary and conclusions

El NiñoEl Niño , La Nina and the Southern Oscillations are coupled , La Nina and the Southern Oscillations are coupled phenomenon that occurs periodically at the Pacific Ocean. phenomenon that occurs periodically at the Pacific Ocean.

Normally, SST and SSH at the eastern pacific is lower than Normally, SST and SSH at the eastern pacific is lower than the western pacific. the western pacific.

During El NiñoDuring El Niño , it’s the opposite of the normal conditions. , it’s the opposite of the normal conditions. SST and SSH rises in the eastern pacific and easterlies SST and SSH rises in the eastern pacific and easterlies slows down or changes direction.slows down or changes direction.

La Niña is the extreme of the normal conditions. SST at the La Niña is the extreme of the normal conditions. SST at the east coast decreases more than usual. east coast decreases more than usual.

Both La NiñaBoth La Niña and El Niñoand El Niño effects the global climate and the effects the global climate and the economy of many countries. economy of many countries.




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Thank you for Listening!!Thank you for Listening!!Questions?Questions?

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