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. In a normal year, in the Pacific Ocean, the trade winds blow westward along the Equator and push warm surface waters near Australia and Indonesia. On the other side of the Pacific Ocean, nutrient-rich cold waters come up off the coast of central and South America, creating favorable conditions for fishing. During an El Niño event, the trade winds weaken and warm, nutrient-poor waters are not pushed anymore by the winds, and sea level rises in the eastern tropical Pacific and falls 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. This causes higher sea level in the western tropical Pacific and lower sea level in the eastern tropical Pacific.
What are we looking at?
The plot tracks the conditions in the Pacific Ocean, showing how El Niño-like or La Niña-like the Pacific Ocean is both right now and in the past. 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. The magnitude of the time series represents the strength of the El Niño or La Niña event.
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