In normal years , atmospheric pressure is greater in the eastern Pacific than in the western Pacific.

The trade winds blow surface water from east to west.

Warm water "piles up" in the western Pacific and sea level is higher than it is in the east.

Upwelling of cold, nutrient-rich water occurs along the western coast of South America

More nutrients = more phytoplankton = food fishing

First noticed off coast of Peru around Christmas, El Niño refers to the Christ child◦ Occurs every 2 – 7 years

Unusual and atmospheric conditions◦ Trade winds slack off or reverse◦ Warm water moves eastward◦ Upwelling slacks off or stops completely

Compare the thermocline from normal conditions (above) to El Niño (below)

Western Pacific (ex. Indonesia) does not get rain◦ No monsoon season ◦ Drought◦ Fires

Eastern Pacific (ex. South America)◦ Tropical thunderstorms◦ Flooding

Opposite effects of El Niño

Stronger winds

Colder temperatures

El Niño Warmer ocean temps

Occurs every 3-7 years

Wetter than normal summers

Weak trade winds

Fewer Atlantic hurricanes

La Niña Colder ocean temps

Frequency unknown

Drier than normal summers

Strong trade winds

Increased hurricane activity in Atlantic