El Niño / Southern Oscillation (ENSO)

1. El Niño / SouthernOscillation(ENSO) By Sagar Bora University of Bremen

2. Outline • Motivation/History • El – Niño/La Niña definition • Normal Conditions in the Pacific Ocean • El – Niño Conditions • La-Niña Conditions • Effects of El – Niño and La-Niña • El – Niño facts • Summary Presented by Sagar Bora

3. 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 itEl Niño, in reference to the Christ child. Presented by Sagar Bora

4. Southern 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. Presented by Sagar Bora

5. ENSO 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. Presented by Sagar Bora

6. Why should we study El Niño? • Reduced upwelling off the coast of South America. So periodic failure of fishery near Peru, which normally is responsible for one-fifth of global fish production. High coral mortality • Drought in South-east Asia, India, Australia and Africa • Heavy rainfall in the South Americas Presented by Sagar Bora

7. El – Niño definition From: www.weathersa.co.za El Niño : When the three-month running mean of the Sea Surface Temperature anomalies in the Nino 3.4 region are greater than or equal to 0.5°C, an El Niño event is assumed to be taking place. Presented by Sagar Bora

8. La Niña definition From: www.weathersa.co.za La Niña: When the three-month running mean of the Sea Surface Temperature anomalies in the Nino 3.4 region are greater than or equal to -0.5°C, an La Nina event is assumed to be taking place. Presented by Sagar Bora

9. Normal Conditions in the Pacific Ocean • Nutrient rich cool water along the Peruvian coast (eastern pacific) due to upwelling; good for marine life; • Shallow mixed layer; thermocline raised • 3 to 8 °C warmer water in the west Pacific near Australia, Indonesia • Deep mixed layer; thermocline pushed down From: www.weathersa.co.za Presented by Sagar Bora

10. Normal Conditions in the Pacific Ocean Source: http://www.wrh.noaa.gov/fgz/science/elnino.php?wfo=fgz Presented by Sagar Bora

11. Normal Conditions in the atmosphere • High pressure in the east above the cold water, low pressure in the west above the warmer water • Pressure gradients result in easterly trade winds which in turn results in upwelling along the Peruvian coast • Trade winds brings moist warm air towards Indonesian region which rises and travels eastward before sinking in the east. This is a thermally direct circulation found by Sir G. Walker. From: www.weathersa.co.za Presented by Sagar Bora

12. El – Niño Conditions in the atmosphere Easterly winds weakens, even changes directions sometimes and becomes westerlies due to change in the sign of pressure gradient. Sir Walker called this east-west seesaw in southern Pacific pressure “Southern Oscillation” From: www.weathersa.co.za Presented by Sagar Bora

13. El Niño conditions in the Pacific Ocean • Due to change in the wind direction, the currents on the ocean also slows down or changes direction from westward to eastward. • SST rises in the eastern pacific and the western pacific cools down a bit; Downwelling occurs off the coast of Peru; nutrient-less warm surface water leads to decline in marine life • Rainy conditions move with the warmer SST and dry conditions move with the cold From: www.weathersa.co.za Presented by Sagar Bora

14. El Niño Conditions in the Pacific Ocean Source: http://www.wrh.noaa.gov/fgz/science/elnino.php?wfo=fgz Presented by Sagar Bora

15. A normal year and an El Niño year Source: http://www.wrh.noaa.gov/fgz/science/elnino.php?wfo=fgz Presented by Sagar Bora

16. La Niña conditions • During La Niña years, the upwelling off the Peruvian coast is enhanced and the SSTs in the Nino regions become cooler than usual. • The Walker Circulation operates in the same way as described for normal years, but because of the larger area of colder water off the South American coast and the displacement of warmer water to the west, the atmospheric pattern also shifts accordingly. Heavier rainfall over Australia and Indonesia and dry spans over South Americas From: http://www.wrh.noaa.gov/ Presented by Sagar Bora

17. La Niña conditions in the Pacific Ocean Source: http://www.wrh.noaa.gov/fgz/science/elnino.php?wfo=fgz Presented by Sagar Bora

18. Global impacts of El Niño Source: http://www.wrh.noaa.gov/fgz/science/elnino.php?wfo=fgz Presented by Sagar Bora

19. Global impacts of La Niña Source: http://www.wrh.noaa.gov/fgz/science/elnino.php?wfo=fgz Presented by Sagar Bora

20. El Niño facts • ENSO is not a weather anomaly, it’s a part of a cycle. • Every weather anomaly throughout the world that occurs during an El Niño year is 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). Presented by Sagar Bora

21. Summary and conclusions • El Niño, La Nina and the Southern Oscillations are coupled phenomenon that occurs periodically at the Pacific Ocean. • Normally, SST and SSH at the eastern pacific is lower than the western pacific. • During El Niño, it’s the opposite of the normal conditions. SST and SSH rises in the eastern pacific and easterlies slows down or changes direction. • La Niña is the extreme of the normal conditions. SST at the east coast decreases more than usual. • Both La Niñaand El Niñoeffects the global climate and the economy of many countries. Presented by Sagar Bora

22. Thank you for Listening!!Questions? Presented by Sagar Bora