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Ocean Circulation:El Niño
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 ChristmastimeSouthern Oscillation = change in atmospheric pressure over Pacific Ocean accompanying El NiñoENSO describes a combined oceanic-atmospheric disturbance
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?
Normal conditions in the Pacific Ocean
Figure 7-18a
El Niño conditions (ENSO warm phase)
Figure 7-18b
La Niña conditions (ENSO cool phase; opposite of El Niño)
Figure 7-18c
Anomaly maps
Anomaly (a = without, nomos = law) maps show the difference from normal conditionsSea Surface Temperature (SST) anomaly maps are useful for identifying unusually warm or cool water:Positive SST anomaly values = water warmer than normalNegative SST anomaly values = water cooler than normal
January 1998 SST anomaly map
Figure 7-19a
January 2000 SST anomaly map
Figure 7-19b
Offshore California
SST anomaly map:
January 1998
Offshore California
SST anomaly map:
January 1999
(1 year later)
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)
El Niño recurrence interval
Typical recurrence interval for El Niños = 2-12 yearsPacific has alternated between El Niño and La Niña events since 1950
Figure 7-20
Pg. 221
Effects of severe El Niños
Figure 7-21
Forecast SST anomalies: Can we expect another El Niño year?
9-month forecast of tropical Pacific SST anomalies
Alternate link for 9-month forecast of tropical Pacific SST anomalies (from Palomar Oceanography Home Page)
End of El Niño presentation
