2. Ocean Circulation: El Niño

3. El Niño-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

4. Questions about El Niño What does an El Niño have to do with the price of eggs? What is La Niña? What kind of weather does El Niño bring to southern California? Is this an El Niño year?

5. Normal conditions in the Pacific Ocean

6. El Niño conditions (ENSO warm phase)

7. La Niña conditions (ENSO cool phase; opposite of El Niño)

8. 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

9. January 2000 SST anomaly map

10. Offshore California SST anomaly map: January 1998

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

12. El Niño/La Niña & 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)

13. El Niño recurrence interval Typical recurrence interval for El Niños = 2-12 years Pacific has alternated between El Niño and La Niña events since 1950

14. Effects of severe El Niños