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El Niņo: Cycle C

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1). El Niño is a warming of the Pacific Ocean between South America and the Date Line, centered directly on the Equator, and typically extending several degrees of latitude to either side of the equator.

2). La Niña is essentially the opposite of El Niño. La Niña exists when cooler than usual ocean temperatures occur on the equator between South America and the Date Line. The name La Niña ("the girl child") was coined to deliberately represent the opposite of El Niño ("the boy child").

3). Among El Niño's consequences are increased rainfall across the southern tier of the US and in Peru, which has caused destructive flooding, and drought in the West Pacific, sometimes associated with devastating brush fires in Australia.

4). 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 Ecuador.

5). 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.


Scenario: El Niño, Spanish for the "Christ child," was originally the name used by fishermen to describe a warming of the Pacific Ocean off the coast of Peru that normally takes place around Christmas time. This warming occurs almost every year and lasts a few weeks. In the relatively recent past, however, scientists have discovered this warming can occasionally last for many months, sometimes even longer than a year, and extend westward along the Equator. Today, when we speak of El Niño, we are usually referring to this longer-term event.

El Niño and its opposite phenomenon -- La Niña -- are part of a cycle of repeated warming and cooling of the ocean surface along the Equator in the central and eastern Pacific. The cycle is known as the El Niño Southern Oscillation (ENSO). El Niño refers to the warm phase of the oscillation and La Nina refers to the cool phase. The Southern Oscillation refers to the fluctuation in pressure above the equatorial eastern and western Pacific. During an El Niño, pressure falls in the east and rises in the west. Since air tends to flow from high pressure toward low pressure, this causes winds that normally blow from east to west across the equator to slow down or even reverse direction. The opposite is true during La Niña, when east-to-west winds increase in strength.

Each of these phases influences weather patterns worldwide and results in changes in rainfall that can alter vegetation patterns. El Niño's impacts include changes in global precipitation that sometimes contribute to flooding or drought. Although scientists have a general idea of the regional weather changes that are typically associated with an El Niño, there are many exceptions to the long-term averages. When an El Niño is weak or moderate, it is especially difficult to predict its impacts. For example, the Los Angeles area normally has above-normal rainfall during weak to moderate El Niños, but during the El Niño of 2006-2007, the area experienced its driest year (July 2006-June 2007) on record.

El Niño has also been linked to: disease in South America, increased atmospheric carbon dioxide and methane from fires, harm to coral reefs, an absence of major hurricanes in the North Atlantic, a link to sea ice changes in Antarctica, and economic implications for the United States.


Author: Bob Myers, IGES



Date: 12/6/2012


Scenario Images

El Nino Southern Oscillation
El Nino is an oscillation of the ocean-atmosphere system in the tropical Pacific having significant consequences for weather around the globe. Among these effects are increased rainfall across the southern portion of the US and in Peru. El Nino, also referred to as ENSO (El Nino Southern Oscillation)has caused destructive flooding, and drought in the West Pacific; it is sometimes associated with devastating brush fires in Australia. Observations of conditions in the tropical Pacific are considered essential for the prediction of short term (a few months to 1 year) climate variations. Go here to compare normal, El Nino and La Nina conditions. Image courtesy of NOAA



  • Science
    National Science Education Standards - Science Content Standards The science content standards outline what students should know, understand, and be able to do in the natural sciences over the course of K-12 education.
      • Science in Personal and Social Perspectives (Std F)
        • Changes in environments
      • History and Nature of Science (Std G)
        • Science as a human endeavor
      • Physical Science (Std B)
        • Motions and forces
      • Earth and Space Science (Std D)
        • Structure of the earth system
      • History and Nature of Science (Std G)
        • Science as a human endeavor
      • Earth and Space Science (Std D)
        • Energy in the earth system
      • History and Nature of Science (Std G)
        • Science as a human endeavor

Individual Assignment
Classroom Application Cycle

This cycle you will develop cooperative activities that engage your students in understanding Earth as a system through analyzing the causes and effects of the event in this module. You also have the option of choosing a Local Event as the focus of your application. Use the resources listed below to develop your ideas. Submit your ideas for your teammates to rate and for your instructor to grade.



  • Review the Individual Classroom Application and Rubric.
  • Create or adapt activities to help your students develop the concepts you have explored in this module. You may choose to do a Local Event Analysis for extra credit this cycle and then base your Classroom Application on it. If you choose to do a local event analysis and then also develop it for your classroom application, you can satisfy this cycle's requirements and receive extra credit.
  • After submitting your own classroom application to the course discussion space, recruit a classmate to rate and make comments on your classroom application. Refer to the Classroom Application Goal and Rubric.

Upload to ESSEA your classroom application with a description of its relevance to students, connection to the curriculum, instructional strategy and assessment methods. Include a reflection on what and how you have learned about Earth System Science and this event as a result of this module. Complete the rubric.
Deadline: Tuesday, January 31 2017 11:59 PM (Eastern Time)
Upload Assignments

Assessment is unavailable

National Geographic's Ocean and Weather: El Nino and La Nina. (Cycle C)
In this lesson students explore the phenomena El Nino and La Nina.
Difficulty: intermediate

Ocean Impacts of an El Nino Event (Cycle C)
Purpose: To examine the relationships among sea surface height, sea surface temperature, and wind vectors in classifying the ocean characteristics of an El Nino.
Difficulty: intermediate

Visualizing El Nino (Cycle C)
Links to several NASA visualizations and animations related to El Niño.

Comments and Questions:
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