Schematic diagrams of El Niño, Normal and La Niña conditions

• The left side of each diagram is the western Pacific Ocean, near Asia, and the right side is the eastern Pacific Ocean, near South America.
• Red/orange colors indicate warm ocean surface temperatures, yellow/greenish colors indicate cooler temperatures.
• The blue band is the "thermocline", approximately the location of water that is about 20ºC (50ºF).
• Rain clouds form over the pool of warm water.

During El Niño, the warm pool of water moves eastward and the slope of the thermocline flattens.
During La Niña, the warm pool moves westward, and the slope of the thermocline steepens.