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Understanding El Niño and La Niña Weather Phenomena

Learn about El Niño-Southern Oscillation (ENSO) - the warm El Niño phase and cool La Niña phase, their effects on weather patterns globally, and recurrence intervals since 1950. Discover how to identify anomalies using SST maps.

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Understanding El Niño and La Niña Weather Phenomena

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  1. El Nino and La Nina

  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. Normal conditions in the Pacific Ocean Figure 7-18a

  4. El Nino conditions (ENSO warm phase) Figure 7-18b

  5. La Nina conditions (ENSO cool phase; opposite of El Nino) Figure 7-18c

  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. January 1998 SST anomaly map Pg. 220 Figure 7-19a

  8. January 2000 SST anomaly map Pg. 220 Figure 7-19b

  9. Offshore California SST anomaly map:January 1998

  10. Offshore California SST anomaly map:January 1999(1 year later)

  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. 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. Effects of severe El Nino Pg. 222 Figure 7-21

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