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Visualization Exercise

El Niño-Southern Oscillation (ENSO)

El Niño is characterized by unusually warm ocean temperatures in the eastern and central Equatorial Pacific, as opposed to La NiƱa, which is characterized by unusually cold ocean temperatures in the eastern and central Equatorial Pacific. El Niño is an oscillation of the ocean-atmosphere system in the tropical Pacific having important consequences for weather around the globe.

In normal, non-El Niño conditions, the trade winds blow towards the west across the tropical Pacific Ocean. These winds pile up warm surface water in the west Pacific Ocean raising sea surface levels about 1/2 meter higher at Indonesia than at Ecuador. During El Niño conditions, the trade winds decrease in the central and western Pacific Ocean leading to a return of warm water eastward. Consequently, the warm water generates greater evaporation and increased rainfall particularly along the west coast of the Americas. At the same time cooler water over the western equatorial Pacific brings drier conditions to Indonesia and Australia.

A measure of the El Niño cycle is the Southern Oscillation, also called ENSO. ENSO is the atmospheric response to the warming or cooling of the equatorial Pacific Ocean. Since a weakening of the trade winds signals an El Niño event, there needs to be lower pressure than normal in the eastern Pacific and higher pressure than normal in the western Pacific. On the contrary, higher pressures to the east cause stronger trades and lead to La Niña conditions. This shift between El Niño and La Niña and its accompanying pressure changes can be measured by the pressure difference between Darwin, Australia (western Pacific) and Tahiti (eastern Pacific), which is known as the Southern Oscillation Index.

In this activity, we examine El Niño, La Niña and the Southern Oscillation and how the ocean interacts with weather and climate. To familiarize yourself with ENSO, look over these references before answering the questions:



For sea surface temperatures (SST) in the last year, look at the website http://www.esrl.noaa.gov/psd/map/clim/sst.anim.year.html


The above animation shows weekly average Sea Surface Temperatures (SSTs) for the past 52 weeks (2014-2015). The various colors represent different temperatures in °C. The bar graph at the bottom left-hand corner shows temperature ranges from 0°C (blue) up to 30°C (red). The X-axis (horizontal axis) represents longitudinal lines with 180° at the center, the western hemisphere to the right, and the eastern hemisphere to the left. The Y-axis (vertical axis) represents latitudinal lines with the equator (0°) at the center, the northern hemisphere above, and the southern hemisphere below. Press “play” to watch the animation. Pay close attention to the center of the animation, which shows changes in the average SSTs in the Pacific Ocean and the date in the upper right-hand corner.

  1. SSTs shift _____ from summer to winter in the northern hemisphere.
    1. further south
    2. further north
    3. further east
    4. further west

  2. Along the equatorial Pacific Ocean, warmer waters are found:
    1. further east
    2. further west
    3. further north
    4. further south

  3. In the summer months of June and July, the warmest SSTs are found in the ______.
    1. western Pacific north of the equator
    2. western Pacific south of the equator
    3. eastern Pacific, north of the equator
    4. eastern Pacific, south of the equator

  4. In the winter months of December and January, the warmest SSTs are found in the _____.
    1. western Pacific north of the equator
    2. western Pacific south of the equator
    3. eastern Pacific, north of the equator
    4. eastern Pacific, south of the equator

  5. Hurricane season in the North Atlantic starts on June 1st. Are the SSTs warm enough anywhere in the North Atlantic Ocean to generate a hurricane (minimum temperatures for hurricane development is about 28 °C) on June 1st?
    1. No, not yet
    2. Yes
    3. Cannot tell from the map

  6. Tropical storm Ana occurred in the North Atlantic in May 2015. Were SSTs warm enough anywhere in the N) Atlantic Ocean before June?
    1. No, not yet
    2. Yes
    3. Cannot tell from the map

  7. From the 2014-15 animation, which month had the highest SSTs in the Caribbean (the islands just south of the state of Florida) in the US which would favor tropical storm development?
    1. June
    2. July
    3. August
    4. September
    5. October

  8. Australia’s hurricane season, which are called typhoons or cyclones because it is located in the Western Pacific as well as Indian Oceans, occur from:
    1. November-April
    2. July-September
    3. October-January
    4. all year long

  9. In the United States, the summer months of the west coast SSTs are _______ than the corresponding summer months of the east coast SSTs.
    1. warmer
    2. cooler
    3. about the same at the same latitudes

  10. The British Isles which are seen at the right upper edge of the map at 55-60oN and 0o longitude are about the same latitude as Eastern Canada (approximately 60°W and 50°N), yet their climate is much milder, especially in winter. This is because:
    1. there is more sunshine in Britain
    2. there is less snow there
    3. the Gulf Stream bring warmer water to NW Europe
    4. the Norwegian current bring warm water south

  11. West coasts of continents near 30°N and S tend to have ___ than east coasts of continents.
    1. cooler ocean currents
    2. warmer ocean currents
    3. some have cooler, while others warmer currents

For information about SST temperatures and anomalies for the last 3 months, SSTs in ENSO regions for past year, use the website



For question #12, view SST anomalies by moving your cursor over “SST Anomalies - Tropical Pacific” located at the upper, center header) The above animation depicts anomalies that occur along the equatorial Pacific Ocean) Anomalies are defined as deviations or departures from normal temperatures) Anomalies range from -3°C (blue), to no anomalies (white), to +3°C (red) as shown on the vertical scale to the right of the animation)

For questions #13-17, click on “Nino Regions Anomalies” to view graphical representations of departures from normal along the equatorial Pacific Ocean. The X-axis (horizontal scale) represents time in months) The Y-axis (vertical scale) represents anomalies with negative values (lower values than normal) in blue and positive values (higher values than normal) in yellow. The solid line indicates the actual SST anomaly.

  1. Looking at the SST anomalies animation of the equatorial Pacific Ocean (SST values above or below normal), which part of the equatorial Pacific has warmer than normal SSTs in September 2015?
    1. western equatorial Pacific Ocean
    2. eastern equatorial Pacific Ocean
    3. both are about the same

  2. Click on the Niño Regions Anomalies. Regions 1 through 4 represent equatorial Pacific locations from South American coast to central Pacific. Which Niño region had the most positive SST anomalies in late 2015?
    1. Niño 1&2
    2. Niño 3 and 3.4
    3. Niño 4
    4. all are about the same

  3. El Niño is defined as SST anomalies above 0)5°C for at least 3 months in Nino 3)4) Which month in 2015 did an El Niño SST anomaly first occur?
    1. July 2015
    2. August 2015
    3. September 2015
    4. all of 2015

  4. In Nino 3.4, when was the largest positive SST anomaly month in 2015?
    1. June
    2. July
    3. August
    4. September

  5. Scroll down the webpage to “Diagnostic and Attribution Tools” and click on the link relating temperature, precipitation in the US to El Niños. In general it shows that during El Niño events, winter (DJF-months December through February) temperatures and precipitation is:
    1. cooler,wetter to the north, drier, warmer to the south
    2. cooler, wetter to the south, warmer, drier to the north
    3. warmer, wetter to the north, cooler, drier to the south
    4. warmer, wetter to the south, cooler, drier to the north

  6. In winter, _______.
    1. California and Florida are wetter than normal during El Niños
    2. California and Florida are wetter than normal during La Niñas
    3. California and Florida usually normal during both El Niños and La Niñas

From the figure below, answer question 18.

  1. Based on late August to mid-September 2015 sea surface temperature anomalies, there is at this time a _______.
    1. major La Niña
    2. major El Niño
    3. minor La Niña
    4. minor El Niño

Please click here for the answers to this exercise.

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