A reversal of airflow between normally low atmospheric pressure over the western Pacific; the cause of El Nino.

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Multiple Choice

A reversal of airflow between normally low atmospheric pressure over the western Pacific; the cause of El Nino.

Explanation:
El Niño is driven by fluctuations in atmospheric pressure patterns across the Pacific that alter the prevailing winds, the Southern Oscillation. When the usual low pressure in the western Pacific weakens or shifts, the pressure gradient that drives the trade winds weakens or reverses, changing the near-surface airflow from east-to-west to a more west-to-east direction. This breaks up the normal Walker circulation, reduces upwelling of cold water off the coast of South America, and allows warm surface water to move eastward, creating the warm ocean conditions that define El Niño. The other options describe ocean currents, not the atmospheric pressure changes and wind reversals that cause El Niño.

El Niño is driven by fluctuations in atmospheric pressure patterns across the Pacific that alter the prevailing winds, the Southern Oscillation. When the usual low pressure in the western Pacific weakens or shifts, the pressure gradient that drives the trade winds weakens or reverses, changing the near-surface airflow from east-to-west to a more west-to-east direction. This breaks up the normal Walker circulation, reduces upwelling of cold water off the coast of South America, and allows warm surface water to move eastward, creating the warm ocean conditions that define El Niño. The other options describe ocean currents, not the atmospheric pressure changes and wind reversals that cause El Niño.

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