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Presentation El Nino


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Presentation El Nino

  1. 1. El Niño and La Niña Two climate mysteries What causes them? Why do they occur?
  2. 2. What is El Niño? <ul><li>A disruption of the ocean-atmosphere system in the Tropical Pacific having important consequences for weather and climate around the globe </li></ul><ul><li>Typically, the ocean surface warms up by a few degrees </li></ul><ul><li>At the same time, the place where huge thunderstorms occur on the equator moves eastward </li></ul>
  3. 3. What is El Niño? <ul><li>Generally affects Northern Hemisphere in the winter </li></ul><ul><li>Originates around equator </li></ul><ul><li>Historically, it has occurred at irregular intervals of 2-7 years </li></ul>
  4. 4. The first signs of an El Niño <ul><li>A rise in air pressure in the Indian Ocean, Indonesia, and Australia </li></ul><ul><li>A fall in air pressure over Tahiti and the rest of the central and eastern Pacific Ocean </li></ul><ul><li>The trade winds in the South Pacific weaken or head east </li></ul><ul><li>Warm air rises in Peru </li></ul><ul><li>Warm water spreads from the West Pacific and the Indian Ocean to the East Pacific. It takes the rain with it, causing rainfall in normally dry areas and drought in normally wet areas. </li></ul>
  5. 5. Under normal conditions, easterly trade winds move water and air warmed by the sun towards the west This also creates an upwelling of nutrient-rich cold water along the coasts of Peru and Ecuador
  6. 6. What the heck is a thermocline? <ul><li>A layer within a body of water or air where the temperature changes quickly with depth </li></ul><ul><li>a heating cycle often fueled by the sun in which a liquid or gas within a closed system is heated and rises </li></ul>What about a convective loop?
  7. 7. Under El Niño conditions, warm, nutrient-poor water slumps towards the east because of weakening winds The nutrient-rich cold water does not get pulled up as much
  8. 8. El Niño’s warm current of nutrient-poor tropical water replaces the cold, nutrient-rich surface water where Peru’s fishing industry usually is vibrant
  9. 10. But it doesn’t stop there! The warmer ocean then affects the winds, and makes the winds weaker. So if the winds get weaker, then the ocean gets warmer, which makes the winds get weaker. This is called positive feedback, and it’s what makes El Niño grow.
  10. 11. But it doesn’t stop there! What stops positive feedback are Rossby waves When El Niño gets going in the middle or eastern part of the Pacific, it creates Rossby waves that drift slowly towards southeast Asia. After several months of traveling, the finally get near the coast and reflect back. The changes in interior ocean temperature that these waves carry with it “cancel out” the original temperature changes that made the El Niño in the first place
  11. 12. The Effects of El Niño are Worldwide
  12. 13. The Effects of El Niño are Worldwide <ul><li>Wet winters over southeastern United States </li></ul><ul><li>Drought in Indonesia and Australia, and other places that are typically wet </li></ul><ul><li>Flooding in South America in areas typically dry </li></ul><ul><li>Wildfires and mudslides </li></ul><ul><li>Warmer winters in the upper Midwest states and Canada </li></ul>
  13. 14. El Niño historically <ul><li>ENSO conditions seem to have occurred at every two to seven years for at least the past 300 years, but most of them have been weak. </li></ul><ul><li>Archaeological evidence in Peru that suggests it has occurred for thousands of years </li></ul><ul><li>A recent study of El Niño patterns suggests that the French Revolution was caused in part by the poor crop yields of 1788-89 in Europe, resulting from an unusually strong El-Niño effect between 1789-93 </li></ul><ul><li>The El Niño of 1997 - 1998 was particularly strong and brought the phenomenon to worldwide attention </li></ul>
  14. 15. How well can we predict El Niño? <ul><li>Satellite readings from buoys strategically set in the Pacific Ocean </li></ul><ul><li>Complex computer models </li></ul>
  15. 16. El Niño vs. La Niña <ul><li>El Niño </li></ul><ul><li>Unusually warm ocean temperatures in eastern Pacific </li></ul><ul><li>Usually more intense effects than La Niña </li></ul><ul><li>Summers in Omaha tend to be wetter and cooler </li></ul><ul><li>La Niña </li></ul><ul><li>Unusually cold ocean temperatures in eastern Pacific </li></ul><ul><li>Usually follows El Niño, but not always </li></ul><ul><li>Summers in Omaha tend to be drier and warmer </li></ul>
  16. 17. El Niño vs. La Niña <ul><li>El Niño </li></ul><ul><li>Causes drier weather on West Pacific seaboards, and wetter, humid weather in the East Pacific </li></ul><ul><li>Warmer winters in the upper Midwest states and Canada </li></ul><ul><li>Wet winters over southeastern United States </li></ul><ul><li>La Niña </li></ul><ul><li>Causes wetter weather on West Pacific seaboards and drier weather in East Pacific </li></ul><ul><li>Colder winters in the upper Midwest states and Canada </li></ul><ul><li>Dry winters over southeastern United States </li></ul>
  17. 18. La Niña to blame? <ul><li>Recent droughts occurred during latest La Niña </li></ul>
  18. 19. Under La Niña conditions, unusually cold water pushes up in the east Pacific Often follows El Niño
  19. 21. What the heck causes El Niño and La Niña?
  20. 22. Major theories <ul><li>Recharge oscillator: Several mechanisms have been proposed where warmth builds up in the equatorial area, then is dispersed to higher latitudes by an El Niño event. The cooler area then has to &quot;recharge&quot; warmth for several years before another event can take place. </li></ul><ul><li>Western Pacific oscillator: In the western Pacific, several weather conditions can cause westerly wind anomalies. For example, cyclones north and south of the equator force west-to-east winds between. Such wind may counteract the typical easterly flows across the Pacific and create a tendency toward continuing the eastward motion. A weakening in the westward currents at such a time may be the final trigger needed to shift into an El Nino. </li></ul><ul><li>Equatorial Pacific Ocean may tend to be near El Niño conditions, with several random variations affecting behavior. Weather patterns from outside the area or volcanic events may be some such factors. </li></ul><ul><li>Global warming?? </li></ul>