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Education: Student Outcomes

Filtered by outcome: 9-12q3
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Outcome: Explain the influence of the El Niño Southern Oscillation on global weather patterns.
Grade level: 9-12
Theme: ocean circulation
Video: elnino-320.flv

Water vapor is a small but significant constituent of the atmosphere, warming the planet due to the greenhouse effect and condensing to form clouds which both warm and cool the Earth in different circumstances. A key feature of global atmospheric water vapor convection is the Intertropical Convergence Zone, the low pressure region within five degrees of the equator where the trade winds converge and solar heating of the atmosphere forces water-laden air to rise in altitude, form clouds, and then precipitate as rain in the afternoon.

Legend for the water vapor animation, showing separate colorbars for total precipitable water and precipitation.
This visualization shows the global water vapor distribution in gray and white and the global precipitation in yellow every hour from December 20, 1997 to January 14, 1998. The afternoon thunderstorms in the tropics are seen as a flashing yellow region that moves from east to west, following the sun. This is an El Niño period, when the water to the west of South America is warmer than normal, allowing the atmosphere there to heat up and hold more water. This region feeds a high band of water vapor reaching to the southeastern United States and causes increased humidity and rainfall in that region.

These data are from the Goddard Earth Modeling System, a coupled land-ocean-atmosphere model which uses earth and satellite-based observations to simulate the Earth's physical system during events such as El Niño. (source)

Compare this video with Components of the Water Cycle: Flow of Atmospheric Water Vapor.
Grade level: 9-12
Theme: ocean circulation

While we inhabit land on the Earth we sometimes forget that we live on a planet where 70 percent of the Earth is covered with water. The variation in the properties of the land versus the water contributes to our global circulation patterns. Sometimes these global circulation patterns are disrupted and we observe the effects of these disruptions in events such as El Niño and La Niña.

It is believed that El Niños occur every two to eight years, and are sometimes stronger, sometimes weaker. This often happens when the southeast trade winds weaken or even reverse. As a result, large masses of water from the western Pacific Ocean migrate to the east to the coast of South America. This change in ocean circulation not only impacts the weather and climate in South America, but also affects locations all around the globe.

These effects can last for about a year, when the opposite conditions occur as the trade winds strengthen again, and the waters off the coast of South America are colder than normal from active upwelling occurring along the coast. This phase of the global circulation disruption is called La Niña.

We have been fortunate over the last 30 years to have satellite and buoy data to warn us if the El Niño phase is upon us. By measuring sea surface heights with satellites like TOPEX Poseidon, sea surface temperature with satellites like AVHRR, and wind vectors from buoys and satellites, we can monitor the Pacific Ocean for changes that may signal the onset of El Niño or La Niña. The sensitive altimeter on the TOPEX Poseidon satellite can measure small changes that create hills and valleys on the sea surface which is mostly caused by thermal expansion (steric effect), and the warming of the ocean during an El Niño event can be sensed by the altimeter.

This lesson explores El Niño by looking at sea surface temperature, sea surface height, and wind vectors in order to seek out any correlations there may be among these three variables. It employs group work where different teams work together to analyze a single variable, and then get together in different groups to compare all three variables. The lesson will guide students through data representing the strong El Niño from 1997 to 1998. By doing this, students will model the methods of researchers who bring their expertise to study integrated science questions. Depending on the classroom dynamics, available technology, and available time, this lesson may be modified.
Grade level: 9-12
Theme: ocean circulation

NASA-sponsored scientists have discovered that by knowing the salt content of the ocean's surface, they may be able to improve the ability to predict El Niño events. Scientists, studying the western Pacific Ocean, find regional changes in the saltiness of surface ocean water correspond to changes in upper ocean heat content in the months preceding an El Niño event. Knowing the distribution of surface salinity may help predict these events.

This study, conducted for NASA by University of Maryland researchers Joaquim Ballabrera, Tony Busalacchi, and Ragu Murtugudde, is one of the first to look at ocean salinity in El Niño, Southern Oscillation (ENSO) predictions and their relationship to tropical sea surface temperatures, sea level, winds, and fresh water from rain.
Grade level: 9-12
Theme: ocean circulation

Activity 4.8: Reversing Rods (p. 40-41). Most substances expand when heated and contract when cooled. As the temperature of most substances increases, their molecules vibrate faster and move farther apart, occupying a larger space. When these substances are cooled, their molecules vibrate slower and remain closer to each other. Note that freshwater below 4°C actually expands when cooled, a phenomena known as the anomaly of water.

Thermal expansion is the principle by which a liquid thermometer works. In the ocean, thermal expansion is thought to contribute significantly to sea level rise on decadal-to-century-long time scales. However, thermal effects appear to be influenced by decadal climate-related fluctuations, making it difficult to estimate the long-term contribution of thermal expansion to sea level rise. Current estimates suggest that thermal expansion is responsible for 25 percent to 50 perccent of observed sea level rise.

In this activity, we look at thermal expansion using two rods, one made of aluminum and the other made of PVC. When placed in cold water, both rods initially float because their densities are lower than that of the cold water. Over time, the PVC rod gets colder and contracts, which results in a density change. When the density of the rod exceeds that of the water, the PVC sinks. The aluminum rod gets colder too, but aluminum expands and contracts much less than PVC when its temperature is changed by the same amount; therefore, the aluminum rod's density is less affected by the temperature change, and it remains floating. Students will also try this experiment with hot water.

Flash Video | QuickTime Movie
Grade level: 9-12
Theme: ocean circulation
Activity: documents/vtop_oc_variations_el_nino.pdf

An El Niño is thought to be triggered when steady westward blowing trade winds weaken and even reverse direction in the western Pacific Ocean, near New Guinea and Australia. This change in the winds allows the large mass of warm water that is normally located in the western Pacific to move eastward along the equator until it reaches the coast of South America. This displaced pool of unusually warm water affects evaporation and where rain clouds form, altering the typical atmospheric jet stream patterns around the world. Scientists are studying information from satellites and in-water buoys to better understand the causes and effects of an El Niño.

In this activity, students will analyze satellite images of sea surface temperature, sea surface topography, and wind data from an El Niño period and compare and contrast these data with non-El Niño conditions.