El Niño and the Southern Oscillation

1. El Niño and the Southern Oscillation

2. Have you heard of El Nino? 1. Yes, and I have a good understanding of the concept. 2. No. 3. Yes, but I really do not understand the concept.

3. Have you heard of the Southern Oscillation? 1. Yes, and I have a good understanding of the concept. 2. No. 3. Yes, but I really do not understand the concept.

4. Have you ever been in an El Niño? 1. Yes. 2. No. 3. I am not sure.

5. Are we currently in an El Niño? 1. No. 2. Yes. 3. I do not know. 4. I really do not care.

6. Background • First, let’s consider what the normal distribution of sea surface temperatures are.

7. Background • Oceanic surface temperature are largely governed by a combination of solar radiation and surface wind patterns

8. Background • Surface currents bring cool waters up along the west coast of South America

9. Cold Water lies beneath the surface. Why? STABLE on average Units: 35 0/00 means 35 parts salt out of 1000

10. Origins of El Niño • Spanish for ‘Christ Child’ • Originally used by fishermen along the coast of Peru and Ecuador in referring to a warm ocean current appearing near Christmas and lasting a few months

11. El Niño • Fish are less abundant during these warm periods because there is less ‘upwelling’ of cold nutrient-rich water • Fishermen spend more time with their • families

12. El Niño • During some years, however, the water remains especially warm and the break in the fishing season extends into May • The term ‘El Niño’ has become reserved for these extreme events

13. So what makes El Niño unique? • During an El Niño, the trade winds weaken • This allows the warm pool of surface water in the western tropical Pacific to extend farther east, to the Peruvian coast . • Warm water suppresses upwelling of cold, nutrient rich water from below. Occurs every 3-7 years, a result of complex air-sea interaction in tropical Pacific

14. So what makes El Niño unique?

15. Why study El Niño? • Association with unusual weather patterns that affect much of the world and persist for a season or more • Ocean surface temperatures may affect the intensity of individual extreme weather events • El Niños are becoming more frequent: the two strongest on record have occurred during the past 20 years

16. Why study El Niño? • Since the effects of El Nino are global in nature, the costs can be astronomical. • A large portion of the costs are often associated with fires in areas of relatively lush vegetation.

17. Why study El Niño? • Increased oceanic surface temperatures can mean stronger and wetter storms for some parts of the world.

18. El Niño’s economic impact • Economic impact on Peruvian fishing is negative • Seabirds that feed on fish also suffer, along with other parts of the coastal ecosystem

19. More recent El Ninos • About two dozen El Ninos have occurred during the past century • Most raised the ocean temperatures along the South American coast and in a belt extending 9,000 km westward in the South Pacific • The strongest events were 1982-83 and 1997-98 with SSTs raised by 3-4 deg C

20. The most recent El Niño Southern Oscillation Index (as of October 12, 2010): http://www.cdc.noaa.gov/ENSO/

21. Southern Oscillation (SO) • SO is a sea-saw variation of surface pressure between western and eastern equatorial Pacific • Equatorial easterlies alternately weaken and strengthen in response to SO

22. Normal weather pattern in the South Pacific: • Eastern region has little precipitation because of downward motion near the high • Western region has precipitation because of upward motion near the low

23. DARWIN AND TAHITI Two locations: large longitude difference small latitude difference long time record Darwin Tahiti SOI = ‘Tahiti – Darwin’ pressure SOI > 0 La Nina/typical SOI < 0 El Nino

24. El Niño and the Southern Oscillation (ENSO)‏ • When the atmospheric pressure rises in the eastern Pacific, it falls in the western Pacific and vice-versa • Southern Oscillation is the ‘seesaw’ of pressure in the South Pacific

25. Southern Oscillation index La Nina ‘Tahiti – Darwin’ La Nina El Nino El Nino

26. El Niño and the weather So how exactly does El Niño impact the weather?

27. The Walker Circulation

28. El Niño Conditions • The easterly trade winds weaken (or even reverse) • The warm waters of the western tropical Pacific come sloshing back to the east because the trade winds are too weak to sustain the tilted sea level

29. El Niño Conditions • The warm waters of the western tropical Pacific come sloshing back to the east because the trade winds are too weak to sustain the tilted sea level

30. Changes to the Walker circulation during an El Niño

31. El Niño Conditions • The upwelling or rising of the cold nutrient-rich waters off the South American coast ceases • The upward motion, clouds and precipitation moves eastward into the central and eastern Pacific

32. Transition from El Niño to La Niña

33. An animation of sea-surface height, as compared With El Niño Nino index: (http://www.esrl.noaa.gov/psd/people/joseph.barsugli/anim.html)‏ (http://www.cdc.noaa.gov/ENSO/)‏

34. El Nino has global consequences • Droughts in Australia and Indonesia • Warm, rainy weather in the eastern Pacific and South America

35. Wild Fires can be a particular problem in Indonesia • During wildfires during the 1997-1998 El Nino event, over 24.1 million acres were burned

36. Wild Fires can be a particular problem in Indonesia • The massive forest fire in Indonesia in 1997 is estimated to have released between 0.81 and 2.57 gigatonnes of Carbon Dioxide into the atmosphere, which is between 13-40% of the annual carbon dioxide emissions from burning fossil fuels.

37. Wild Fires also represent a huge health hazard. • At one point, the pollution index of the region reached 839. To put a relative point to this number, a pollution index of 300 is the equivalent of smoking 20 cigarettes a day. The smoke, during one time, blanketed an area that was larger than the continental United States.

38. Wildfires and Drought in Australia • Another region severely impacted by droughts and wildfires during an El Nino event is Australia. • The droughts have a severe impact on agriculture, mainly in the form of an inability to feed livestock.

39. Wildfires and Drought in Australia • Also, without the shrubs and pasture land, dust and particulate matter become a significant problem.

40. Flooding and disease • In areas of flooding, water borne diseases become a significant issue. For instance, consider cholera in Peru.

41. Disease and El Nino In very humid climates, droughts may turn rivers into strings of pools, preferred breeding sites of other types of mosquito .

42. El Niño has a large impact on North American weather, including a reduction in Atlantic Ocean hurricane activity, because of the very strong upper-level winds that produce too much wind shear for a hurricane to continue to exist up below

43. The 1998 Ice Storm in Montreal was associated with a record-breaking El Niño

44. Gyakum and Roebber 2001 (Monthly Weather Review)‏ Roebber and Gyakum 2003 (Monthly Weather Review)‏

45. Freezing rain accumulation

47. Effects in California • Effects in California include storm surge and coastal erosion, as well as the possibility of floods and landslides

48. La Niña • Opposite to El Niño • Higher than average pressure in the eastern Pacific and lower than average pressure in the western Pacific

49. La Niña

50. La Niña • Stronger than normal easterly trade winds • Colder than normal ocean temperatures off of South America • Flooding in Australia and Indonesia