El Niño-Southern Oscillation (ENSO) Index

What is El Niño-Southern Oscillation?

El Niño-Southern Oscillation is a climate pattern in the Pacific Ocean that has two phases: El Niño and La Niña. During an El Niño event, the winds that usually push warm waters near Asia weaken causing sea level to rise in the eastern tropical Pacific and to fall in the western tropical Pacific. La Niña is the opposite phase of El Niño with warm water piling up in the western Pacific and colder water in the eastern Pacific causing higher sea level in the western tropical Pacific and lower sea level in the eastern tropical Pacific. The temperature of the water also changes, which causes weather patterns to shift across the globe.

What are we looking at?

The plot tracks the conditions in the Pacific Ocean, when the value of the time series is positive (red shading), El Niño conditions are present, and when the value is negative (blue shading), La Niña conditions are present.

Why do we care?

El Niño affect fisheries, especially in South America where warm, nutrient-poor waters disrupt fishing. Also, both El Niño and La Niña events bring severe weather events. In the Southwestern United States El Niño brings rain, but in Asia and Australia flooding is usually associated with La Nina. Besides the rain, the high sea levels of El Niño and La Niña threaten coastlines with flooding and erosion.

Reference: Hamlington et al., 2019

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