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 ( = 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 ( = 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