Upwelling Currents and El Niño Name:

Objectives:

1) Learn about the processes that create upwelling currents in the ocean and that create the El Niño climatic condition.

2) Understand that upwelling currents and El Niño have profound economic implications for people around the globe.

Go to the Earth Systems Laboratory and open the course web site: http://geosci.sfsu.edu/courses/geol103/labs/.

Click on the Upwelling Currents and El Niño exercise. The questions in this printed exercise correspond with the text and imagery presented in this section of the web site. Space for answers is provided below each question.

PART I. Upwelling Currents

1. Description:

Read through this introductory description of upwelling and examine the Ekman spiral diagram.

2. Coastal Upwelling

(a) Make a simple sketch of the California coastline. A map (bird's eye) view is all that is necessary. Don't forget that California is in the northern hemisphere. Depict on your map the special situation that would create upwelling currents off the coast of California by drawing and labeling arrows to illustrate (1) the direction of the wind and (2) the direction of the surface water.

(b) Using what you have learned about upwelling currents, explain the distribution of pigment concentrations and temperatures along the California coast that is shown in the satellite imagery.

3. Equatorial upwelling

Read this brief section because it will help you understand the equatorial biological activity that is associated with El Niño.

4. World-wide primary productivity

(a) Describe the locations in the ocean that have high productivity values (that is, high pigment concentrations) and explain why values are high at these locations.

(b) Describe the locations in the ocean that have low productivity values and explain why values are low at these locations.

(c) Compare the winter (northern hemisphere) and summer (northern hemisphere) images in terms of high and low productivity regions.

Some aspects of the images to look for when considering your answers: (1) when equatorial upwelling is strongest and why; (2) compare specific coastal locations and speculate about reasons for observed variations; (3) explain seasonal variations in the high latitude regions (near the poles). Remember that productivity depends on both nutrients (often from upwelling currents) and from light (variations particularly important in temperate to high latitudes).

5. Seasonal changes

[NOTE: degrees Fahrenheit = 1.8 (degrees Celsius) + 32]

(a) Based on the satellite images below, would you say that upwelling currents are strongest in January or in July along the coast of northwest Africa? Speculate about possible causes for this seasonal variation. Look at a world map to see the latitudinal position of Africa. The currents exercise contains a map of latitudinal variation in atmospheric winds (generalized).

(b) Compare these images to the global productivity diagrams in the previous section. What do these images suggest about the seasonal variation in equatorial upwelling in the world oceans? Both of these images are from the eastern sides of oceans and both show the "normal" condition that occurs there. In part II of this exercise we will examine a variation of equatorial conditions in the eastern Pacific called "El Niño".


PART II. El Niño

6. Description:

(a+b) Use this table to characterize how ocean/atmosphere characteristics during normal and El Niño conditions differ between the eastern and western sides of the equatorial Pacific. Examine the images in both section (a) and (b) to help clarify some of the major oceanic changes.

Normal / Normal / El Niño / El Niño
west / east / west / east
sea-surface temperatures (SSTs)
winds
areas of rising air
thermocline

(c) What happens to sea-level pressure in the eastern Pacific during El Niño years? (The converse prevails in the western Pacific.)

6. Buoys along the equator

(a) How many moorings (buoys) are deployed in the equatorial Pacific?

(b) How deeply do the buoys sample oceanic water?

7. Data from the equator

(a) Based on what you have learned so far, explain the changes between normal and El Niño years that are illustrated by these data. Keep in mind that these data show only sea-surface conditions (not conditions at depth).

(b) Using the formula below, convert Celsius degrees to degrees Fahrenheit. Show your work on the right, please.

[formula: degrees Fahrenheit = 1.8 (degrees Celsius) + 32]

28 degrees Celsius = ______degrees Fahrenheit

20 degrees Celsius = ______degrees Fahrenheit

15 degrees Celsius = ______degrees Fahrenheit

8 degrees Celsius = ______degrees Fahrenheit

(c) Based on the sea-surface temperatures and winds shown in this diagram, do you think that this was a year of normal or El Niño conditions?

(d) Describe the variations in ocean temperatures from east to west along the equator and from the surface to 500 meters depth during a time of normal conditions in the Pacific Ocean.

(e) Where in the Pacific Ocean were these data collected? (Look at a world map at the appropriate latitude and longitude.) During which months were El Niño conditions strongest during the 2-year period shown in the diagram above?

During which month(s) did El Niño conditions begin?

(f) Do you think the ocean-atmosphere system of our planet is currently in a normal mode, closer to an El Niño state, or closer to a La Niña condition?

8. Global consequences

(a) In each section of the following table, list one location on Earth for each question posed on the web site.

Winter / Summer
Wet
Dry

(b) According to this diagram, which areas of the U.S. show the largest anomalies in precipitation during El Niño?

Which areas of the U.S. show the largest anomalies in temperature during El Niño?

9. 1997 El Niño

(a) How much warmer than normal were surface waters of the eastern equatorial Pacific during the 1982-83 El Niño event?

Which parts of the Pacific Ocean were colder than normal?

(b) During which month(s) do you think we first suspected that El Niño conditions were beginning to develop in the tropical Pacific? (Note that SSTs on the eastern side of the Pacific were colder than normal prior to the onslaught of El Niño.)

(c) Describe changes in the temperatures and winds that occurred within this nine-month period.

(d) At which depths did the greatest temperature anomalies occur in the eastern Pacific?

How much warmer were water temperatures in the eastern Pacific compared to normal years?

Compare this diagram with a similar diagram (part 8 of this exercise) from November 1996.

Briefly describe the differences.

(e) Describe the changes in sea-surface height that occurred during this time period.

What are some of the expected manifestations of this mass of elevated, warm water in the eastern Pacific?

(f) Briefly describe the temperature and precipitation anomalies.

(g) Compare the temperature anomaly diagram from 1997 in part (f) above with the temperature anomaly diagram from 1982-83 in part (a). Does the magnitude of the anomaly seem similar or different?

What is this difference?

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