El Ni ñ o/La Ni ñ a- Short term climatic change

1. El Niño/La Niña- Short term climatic change

2. El Nino/La Nina: A WELCOME or UNWELCOME VISITOR? • P 24-25 Pearson • P 19-20 Philip Allan • 2 x Geofiles (on the blog) http://www.pbs.org/wgbh/nova/elnino/ http://oceanworld.tamu.edu/ http://www.bbc.co.uk/weather/features/el_nino_events.shtml

3. El Nino and La Nina are amongst the most powerful phenomena on the earth as they affect the climate over almost half of the earth. • El Nino (means male child in Spanish) and it refers to a weak warm current appearing around Christmas along the coast of Ecuador and Peru. They happen every 3-4 years and may last from 12-18 months. • Over the last few decades there have been more stronger events and the term El Nino is now linked more closely to these.

4. La Nina (meaning female child in Spanish) refers to an anomaly of cold sea surface temperatures found in the eastern tropical Pacific (by Australia and Indonesia etc) • La Nina episodes may follow El Nino (but not always.

5. What is happening usually?

8. Hadley Cells

10. Normal years

11. Under normal conditions there is high air pressure off the coast of Peru and Ecuador with descending air resulting in the Atacama desert • And there is low air pressure over the western Pacific (Australia and Indonesia) giving heavy convectional rainfall. • This movement of air results in the Walker cell. • The upper air moved west to east and the lower air moves from east to west as the trade winds.

12. Surface water gets pushed westwards …. The sea level is normally 60cm higher in the Philippines than in Panama/Colombia • Water flowing westwards stays warm (28 degrees C in the western Pacific). • Cold water(20 degrees C) that wells up near Peru and Ecuador is rich in plankton and great for fishing.

13. And in El Nino years? • These are scientifically called an El Nino Southern Oscillation (ENSO) and happen every 3-4 years and may last from 12-18 months. • There is a reversal to normal conditions. • Pressure rises over the Western Pacific (Indonesia and Australia) and falls over the Eastern Pacific (Peru and Ecuador)

14. The Inter Tropical Convergence Zone (ITCZ) shifts South and causes trade winds to weaken and maybe even reverse their direction. • Air descends over South East Asia (drier weather) and ascends over the west coast of South America (wetter weather). • The changing trade winds means that sea level in South East Asia tends to fall and it rises in tropical South America. • Surface temperatures to the East is warmer and there is less upwelling of cold water off Peru. Sea temperatures there may rise by 6 degrees C so plankton suffers as does Peru’s fishing industry.

15. Normal Year El Nino

16. Sea Level

19. El Niño Builds, Warm Wave Surges Toward South AmericaNovember 20, 2006

20. Examples of El Nino – 1982-83, 1986, 1992-93, 1997-98 • Effects of El Nino • Change of weather around the world • The very strong El Niño of 1997-98 caused: • South America • High evaporation and precipitation – For each of 12 days in early March Peru got 6 months of normal rain. Flash floods killed 292, injured more than 16,000, destroyed 13200 homes and wrecked roads and farmland. Half a million Peruvians affected. • Economic disaster to the Peruvian fisheries. • Some plants blooms for the first time in 100 years in the Atacama desert • Indonesia and Australia • Droughts in Australia, which caused a water shortage. • Lake Eyre in Australia dried up • Indonesian forest fires caused severe haze over several countries

21. Effects of El Nino in other parts of the world • Other parts of the world • severe coastal storms, heavy rainfall, flooding and mud slides in California on the west coast of the United States. • droughts in Mexico and Central America, which led to forest fires that burned for long periods of time and sent heavy smoke north to the United States • unusually mild winters on the east coast of the United States – very little snow in the Rockies • Heavy rain increases wildlife in Botswana • Late arrival of monsoon in Indian subcontinent • Droughts in SE Asia

22. Sydney Dust Storms Sept 2009 http://www.dailytelegraph.com.au/news/gallery/gallery-e6frewxi-1225778417848?page=7

23. La Nina • The ‘little girl’ is the reverse of El Nino. • It has occurred less frequently than El Nino. • It is less easy to predict due to less evidence. • The low pressure over the Western Pacific (Indonesia and Australia) becomes even lower and the high pressure over the Eastern Pacific (Peru and Ecuador) even higher.

26. Rainfall increases over South East Asia • And drought conditions happen in South America. • The increased difference in air pressure over the Pacific strengthens trade winds. • Larger amounts of water are sent westwards giving higher sea levels in Indonesia • There is an even greater upwelling of cold currents on the Peruvian coast

27. One of the strongest La Niñas blankets the Pacific Ocean near the equator, This La Niña is indicated by the blue area in the centre of the image along the equator. Blue indicates lower than normal sea level (cold water). The data were gathered in early April 2008

28. Effects of La Nina • Scientists believe that la Nina could be linked to greater hurricane activity in the Caribbean. • It also interrupts the jet stream by the mid latitudes, like the UK, giving stormier, wetter and cooler conditions. • See the diagram on the next page.

29. So what do you think: A WELCOME or UNWELCOME VISITOR ? • Essay How does El Nino and La Nina affect weather patterns? (10 marks)