Hatfield Marine Science Center

Pre-visit materials

printable .pdf version available here

Mapping an El Niño

map of climate conditions

Goals, Objectives, and Benchmarks

During this classroom learning experience at the Hatfield Marine Science Center, your students will have the opportunity to study the development of an unusual ocean event, termed "El Niño". This warming of tropical ocean waters has been observed and noted by Peruvian fishermen since the 1500's. Thanks to the establishment of global weather tracking systems, the mysteries of El Niño are just beginning to unfold. Our objective in offering this class is to provide a hands-on exercise that gives students the ability to effectively visualize the development of an El Niño, how it occurs, and its effect on oceans ecosystems.

The goals and objectives for this class are:

  1. Provide the student with an understanding of how oceanographers measure present ocean conditions.
  2. Understand the principles of and be able to determine latitude and longitude.
  3. To be able to read NOAA's computer generated Sea Surface Temperature maps and the contours of isotherms and gather data from them.
  4. Understand the differences between climatology generated "normal" ocean conditions and present "real-time" ocean conditions.
  5. Compare the data and map the anomalies (differences) in color to produce monthly maps exposing the El Niño event.
  6. Follow the development of the 1997-98 El Niño event, learning how it occurs, its impact on ocean conditions, and subsequent effects on marine food chains.

Oregon Education Common Curriculum Goals and Benchmarks

Curriculum Goal:

  • Use analysis and interpretation to formulate explanations and draw reasonable conclusions based on the results of an investigation. Use integrated scientific process skills to predict, design experiments, control variables, interpret data, define operations and formulate models.

Grade 8 Benchmark

  • Evaluate evidence of physical and biological changes over time. Use a model to make predictions and inferences about familiar and unfamiliar phenomena in the natural world.

Grade 10 Benchmark

  • Use conceptual and/or mathematical models to explain natural systems. Propose explanations that are supported by data and knowledge of science concepts and principles.

Grade 12 Benchmark

  • Design and conduct a scientific investigation based on questions or hypotheses related to a current issue. Analyze data collected in a scientific investigation on a current problem or issue and evaluate sources of error and/or bias.

Before Your Visit

  • Review the information in this pre-visit packet with your students.
  • Students should have a basic understanding of latitude and longitude and be able to identify coordinates on a map.
  • Students should be able to locate the tropical Pacific region of the world as this is the site of El Niño.
  • Students should understand the meaning of "normal" ocean conditions as determined by climatologists.
  • Students must have an idea of what an El Niño is and be able to formulate an approximate definition.
  • Students must understand and be able to use terminology from the Glossary.

Mapping El-Niño

chart of ocean anomalies

What is an El Niño? El Niño is a warming of the ocean temperatures in the tropical Pacific having important consequences for weather around the globe. Observations of conditions in the tropical Pacific are considered essential for the prediction of short-term (a few months to 1 year) climate variations. To provide necessary data, NOAA operates a network of buoys, which measure temperature, currents and winds in the tropical Pacific. These buoys transmit data, which is available to researchers and forecasters around the world.

wind and current directions

In normal, non-El Niño conditions, the trade winds blow towards the west across the tropical Pacific. These winds pile up warm surface water in the west Pacific, so that the sea surface is about 1/2 meter higher at Indonesia than at Equador. The sea surface temperature is about 8 degrees C higher in the west, with cool temperatures off South America, due to an upwelling of cold water from deeper levels. This cold water is nutrient-rich, supporting high levels of plant and animal plankton, diverse marine ecosystems, and major fisheries.

heating of surface water
During its journey west, surface water is heated by the sun to temperatures of about 29°C over a huge area west of the dateline, known as the west Pacific warm pool. Here the ocean is roughly 8°C higher than when the water came to the surface in the east.

March-May Normal conditions



December-February Normal conditions

The air is also very humid due to its long passage over the tropical ocean, and when it rises in the west, heavy precipitation is produced over Indonesia, leaving the east Pacific relatively dry.

Easterly winds weaken .,..

During El Niño, the trade winds relax in the central and western Pacific leading to a depression of the thermocline in the eastern Pacific, and an elevation of the thermocline in the west. This reduces the efficiency of upwelling to cool the surface and cuts off the supply of nutrient rich water from below. Lacking strong trade winds, the sea surface level equalizes between Peru and Indonesia dragging warm water with it in an event termed an El Niño/Southern Oscillation (ENSO).

surface temperature rises and plankton declines

The result is a rise in sea surface temperature and a drastic decline in plankton growth, the latter of which adversely affects the marine food chain, including commercial fisheries in this region.



The weakening of easterly tradewinds during an El Niño/Southern Oscillation event is evident in these figures as well. Rainfall follows the warm water eastward, and associated flooding in Peru and drought in Indonesia and Australia. The eastward displacement of the atmosphere overlaying the warmest water results in large changes in the global atmospheric circulation, which in turn force changes in weather in regions far removed from the El Niño waters of the tropical Pacific.

El Nino impacts, June-September 1997

These changes normally involve higher ocean temperatures along North and South America's Pacific coast, but can also include heavy rains in the southwestern US, fewer Atlantic hurricanes, droughts in central Africa and a milder monsoon season in southeast Asia.

The TAO (Tropical Atmosphere Ocean) Array, consisting of nearly 70 moored buoys in the tropical Pacific, measure ocean water and air temperatures and wind direction and speed. These buoys provide climate researchers, weather prediction centers, and scientists around the world with up to date (real-time) data from the tropical Pacific.

Climatology Data - Just What is "Normal"

climatology data example

Climatology data is taken from the buoys and shows the "normal" ocean conditions that we would expect to find during each month. The above chart shows isotherms, or lines connecting areas of similar sea surface temperature (SST) that would be found during a "normal" January. Note the tongue of upwelling cold water in the eastern equatorial Pacific ocean.

Means compared with anomalies

El Niño can be seen in measurements of sea surface temperature, such as those shown above, which were made from the moored buoys. The top chart plots the January, 1998 mean (average) SST's (sea surface temperatures). The bottom chart plots the SST anomalies, or the difference between the normal monthly temperature (climatological mean) and the average temperature for January, 1998.

Information about the names El Niño and La Niña El Niño was originally recognized by fishermen off the coast of South America as the appearance of unusually warm water in the Pacific ocean, occurring near the beginning of the year. El Niño means "The Little Boy" or "Christ Child" in Spanish. This name was used for the tendency of the phenomenon to arrive around Christmas. La Niña means "The Little Girl". La Niña is sometimes called El Viejo, anti El Niño, or simply "a cold event" or "a cold episode". El Niño is often called "a warm event".

Glossary of Terms

Anomaly - the difference between the current SST value and its long term average

Climatology - the science that deals with climates, or the average condition of the weather at a particular place over time, and investigates their phenomena and causes

Isotherm - a line on a map connecting points having the same temperature for a given period of time

Mean - having an intermediate value between two extremes, the average

SST - sea surface temperature, measured at one meter below the surface

Thermocline - a layer of water separating an upper warmer lighter oxygen-rich zone from a lower colder heavier oxygen-poor zone

Color versions of these maps may be found on the World Wide Web at: http://www.pmel.noaa.gov/toga-tao/el-nino

After Your Visit

We recommend everyone take the finished monthly anomaly maps back to the classroom. They can be displayed and discussed as to their accuracy and how well they show the development and progression of the 1997-98 El Niño.

Bibliography

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Last Update: February 4, 2004

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