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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

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.