Investigation 9: El Niño and La Niña
- Page ID
- 43481
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The Atacama Desert, located along the Pacific coast of Chile in South America, is known as one of the driest non-polar deserts in the world (Figure 9.1). The cool Humboldt ocean current sweeps northward along the coast, resulting in less than 15 millimeters (0.6 inches) of rainfall per year in the Atacama Desert. Southerly winds along the coast also promote the upwelling of cold, nutrient-rich waters, which attract large populations of fish, such as anchovies. Thus, fishing is one of the major sources of food and income for the Peruvian people who live just north of this region. However, every few years, something changes. Rainfall increases in the desert, the fish vanish, and the arid desert landscape begins to bloom with a vibrant display of flowers (Figure 9.2). Because this always happens around Christmas in those years, the residents began calling it "El Niño", which in Spanish means "the boy", but in this context, refers to the Christ child.
Whenever it occurs, weather extremes such as droughts, floods, and heatwaves affect people across different continents. While South American countries like Chile and Peru face flooding, Australia and East Asia suffer from droughts and Heatwaves. In Africa, eastern countries like Kenya suffer from increased rainfall and deadly diseases, while southern countries, such as South Africa, face drought. Even Europe is not spared, with northern countries facing colder-than-average winters and southern countries experiencing heavier-than-average rainfall and flooding. Here in the United States, El Niño typically brings warmer, drier winters to the northern U.S. and wetter conditions to the southern U.S., including increased rainfall and flooding in Central and Southern California.
In this Investigation, let's learn more about this global-scale phenomenon that affects the weather worldwide.
By the end of this investigation, you should be able to:
- Describe the El Niño Southern Oscillation
- Identify the 3 phases of the Walker circulation
- Distinguish between the Pacific surface conditions during El Niño, La Niña, and Neutral phases.
- 9.1: The Walker Circulation
- El Niño's connection to the Walker Circulation is explained, along with its impact on global weather, particularly in the Pacific. It describes how the trade winds shift warm water and create pressure differences, resulting in varied weather patterns with stormy conditions in the west and dryness in the east. The significance of the TAO/Triton Array is also highlighted, as it collects crucial data on sea surface temperatures and wind patterns to monitor these phenomena.
- 9.2: El Niño and La Niña Phases
- Both El Niño and La Niña phases of the Walker Circulation are explained. El Niño results from weakened trade winds, leading to warmer eastern Pacific waters and drier conditions in the west. At the same time, La Niña is characterized by intensified trade winds, resulting in cooler eastern temperatures and warmer waters in the west. It also mentions the TAO/Triton buoy array, which is used to monitor these conditions and their significant effects on global weather patterns.
- 9.3: Alternative Text Descriptions for Investigation 9
- This page provides detailed text descriptions of images and charts used in Investigation 9
Thumbnail: Sea surface temperature during El Niño and La Niña. Sea surface temperature anomalies by Steve Albers is licensed under CC BY 3.0