Name:
Upwelling Currents and El Niño
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.
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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).
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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".
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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
west
Normal
east
El Niño
west
El Niño
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).
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(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?
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(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.)
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(c) Describe changes in the temperatures and winds that occurred within this ninemonth 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.
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(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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