During the past 40 years, nine El Niños have affected the South American coast. Most of them raised water temperatures not only along the coast, but also at the Galapagos Islands and in a belt stretching 5000 miles across the equatorial Pacific. The weaker events raised sea temperatures only one to two degrees Fahrenheit and had only minor impacts on South American fisheries. But the strong ones, like the El Niño of 1982-83, left an imprint, not only upon the local weather and marine life, but also on climatic conditions around the globe.
The easterly winds that blow along the equator and the southeasterly winds that blow along the Peru and Ecuador coasts both tend to drag the surface water along with them. The Earth's rotation then deflects the resulting surface currents toward the right (northward) in the Northern Hemisphere and to the left (southward) in the Southern Hemisphere. The surface waters are therefore deflected away from the equator in both directions and away from the coastline. Where the surface water moves away, colder, nutrient-rich water comes up from below to replace it, a phenomenon known as upwelling. Both the equatorial upwelling and the coastal upwelling are concentrated in narrow regions less than 100 miles wide.
The winds that blow along the equator also affect the properties of upwelled water. In the absence of the wind, the dividing layer between the warm surface water and the deep cold water, known as the thermocline, would be nearly flat; but the winds drag the surface water westward.
1. Why are fish populations affected by El Nino? (explain global wind patterns and upwelling in your answer)
2. How can winds affect ocean movement? (be specific!)
El Nino and La Nina on the Reference Tables (Page 4 ESRT)
1. What is the temperature of the South Equatorial Current? (warm or cool?) ______________
2. What is the temperature of the Peru Current? (warm or cool?) ______________
3. What is the direction of the Equatorial Countercurrent? ______________
4. Will the Equatorial Countercurrent bring cool or warm water to Peru? ______________
5 The trade winds between 30ºS and the equator blow in which direction? ______________
Compare and contrast the two diagrams to explain how El Nino years are different from ‘normal’ years
During El Nino years, there tends to be more thunderstorms over Peru. Explain how you get these thunderstorms, starting with the fact that El Nino brings warm, moist water near Peru.
During El Nino, the South Equatorial Current reverses direction and flows over the top of northern portions of the Peru Current. How will this affect the temperature of the North East coast of South America? (use ESRT)
Conclusion (Will be written on whiteboard or smartboard):