1. El Nino and La Nina
Ocean_4_ENSO Lecture

2. Where in the world are we?
El Nino- Occurs in tropical waters (Equatorial Pacific)
El Nino means “The Baby” (not necessarily “the Nino,” but close) because it usually happens around Christmas (connected to the baby Jesus)

3. First, a review of Solar Intensity and Latitude
At low latitudes (near the equator) the sun’s rays are nearly vertical.
At high latitudes (near the poles) the sun’s rays are much less intense because the sun remains close to the horizon
From

4. What causes the seasons?
Earth is tilted by 23.5 degrees
The northern and southern hemispheres each tilt toward the sun for half the year
Hence we have seasons
The equator is unaffected by this

5. Equal amounts of sunlight are spread over a greater area in polar latitudes than in temperate or tropical latitudes.
Tropics
temperate
polar
From

6. The take-home message Tropical latitudes are the warmest
Air rises there
This causes convection cells (Hadley Cells) that constantly move air throughout the atmosphere

7. Because the Coriolis Effect also moves air masses Clockwise in the N Hemisphere (and CCW in the S Hem.), ...
Winds move generally Westward off of South America’s W. Coast
Now back to El Nino...

8. Normal conditions in Pacific
Trade winds blow off the west coast of S. America (movement from high pressure to low pressure)
The movement of warm water into western Pacific forces cold deep water towards the eastern Pacific
Causes area of upwelling on South American coast. Water is cold and nutrient-rich; supports strong fishing industry by providing nutrients for the basis of food chains

9. What do normal Pacific conditions look like?

10. El Nino
Trade winds that move warm water to western Pacific lessen, allowing warm water to move towards eastern Pacific

11. Effects of El Nino Coastal upwelling halts in eastern Pacific ocean
More rainfall with movement of warm water mass to eastern Pacific
Droughts in western Pacific

12. La Nina Also known as the “anti-El Nino” or “El Viejo”
Cold phase of the climate pattern
Higher pressure and trade winds increase towards the western Pacific
Causes more upwelling in eastern Pacific and more rain in western

13. Visual comparison between El Nino and La Nina

14. Duration and impacts of El nino
Occurs every 2-7 years and lasts 12 to 18 months
Triggers weather extremes worldwide
High sea surface temperatures trigger thunderstorms/hurricanes
Coastal fisheries in S. America are devastated without cold upwelling of nutrients
Flooding in typically dry areas ex. S. California
Drought and fire in typically humid areas ex. Indonesia