Final answer:
El Niño is characterized by low air pressure over the western tropical Pacific, weakening of trade winds, and a decrease in upwelling along the west coast of South America.
Step-by-step explanation:
During El Niño, there is unusually low air pressure over the western tropical Pacific. This is because the warm ocean waters in the central and eastern Pacific cause the air to rise, creating an area of low pressure. This results in changes in weather patterns around the world, such as increased rainfall in some regions and drought in others.
Additionally, during El Niño, the trade winds, which are normally strong in the tropical Pacific, weaken or even reverse direction. This weakening of the trade winds can have a significant impact on weather patterns and ocean currents.
Furthermore, El Niño can lead to a decrease in upwelling along the west coast of South America. Upwelling is the process by which cold, nutrient-rich water from the deep ocean rises to the surface. When upwelling decreases, it can have negative effects on marine ecosystems and fish populations.
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