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El Nino & La Nina

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El Nino & La Nina

  1. 1. El Nino and La Nina
  2. 2. El Nino-Southern Oscillation (ENSO) El Niño (Spanish for “the Child” in reference to baby Jesus) = warm surface current in equatorial eastern Pacific that occurs periodically around Christmastime Southern Oscillation = change in atmospheric pressure over Pacific Ocean accompanying El Niño ENSO describes a combined oceanic- atmospheric disturbance
  3. 3. Normal conditions in the Pacific Ocean Figure 7-18a
  4. 4. El Nino conditions (ENSO warm phase) Figure 7-18b
  5. 5. La Nina conditions (ENSO cool phase; opposite of El Nino) Figure 7-18c
  6. 6. Anomaly maps Anomaly (a = without, nomos = law) maps show the difference from normal conditions Sea Surface Temperature (SST) anomaly maps are useful for identifying unusually warm or cool water: Positive SST anomaly values = water warmer than normal Negative SST anomaly values = water cooler than normal
  7. 7. January 1998 SST anomaly map Figure 7-19a Pg. 220
  8. 8. January 2000 SST anomaly map Figure 7-19b Pg. 220
  9. 9. Offshore California SST anomaly map: January 1998
  10. 10. Offshore California SST anomaly map: January 1999 (1 year later)
  11. 11. El Nino/La Nina & weather in southern California Typical weather during El Niño? Strong El Niños: Lots of powerful storms (good waves), lots of rain (1997-1998 = more than double our normal rainfall), but not always… Moderate/Weak El Niños: can have drought conditions or lots of rain or no effect at all Typical weather during La Niña? Extremely dry conditions (2000-2001 = 1/3 normal rainfall)
  12. 12. El Nino recurrence interval Typical recurrence interval for El Niños = 2-12 years Pacific has alternated between El Niño and La Niña events since 1950 Figure 7-20 Pg. 221
  13. 13. Effects of severe El Nino Figure 7-21 Pg. 222

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