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
Figure 7-19a
Pg. 220

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

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
Figure 7-21
Pg.
222