El Niño-Southern Oscillation (ENSO)
Meat & Livestock Australia October 20, 2023
El Niño-Southern Oscillation (ENSO) is a climate pattern that occurs in the Pacific Ocean and is one of the most important climate drivers for a large portion of Australia, impacting both northern and southern regions.
During a period of El Niño, equatorial trade winds weaken and warm surface water shifts to the eastern Pacific Ocean allowing cool water to upwell in the western Pacific Ocean, which can lead to reduced rainfall and drought conditions across northern areas and eastern Australia. In contrast, during a period of La Niña, the trade winds are stronger than average, building up warm surface water in the western Pacific Ocean while cool water upwells in the eastern Pacific Ocean, which can lead to increased rainfall and flooding across impacted regions of Australia.
An active phase of the ENSO usually occurs every 3-5 years, but can happen more frequently.
The following videos explain the impact of ENSO and how it behaves.
Key points
- There are 3 ENSO phases: El Niño (typically dry in winter and spring), neutral (not active), La Niña (typically wet)
- Active ENSO phases usually start in winter, develop in spring, peak in summer and finish in autumn
- We use ocean temperatures in the central and eastern Pacific Ocean and the Southern Oscillation Index (SOI) to know if there is an ENSO event occurring
- SOI values above about +7 indicate a La Niña and below -7 is an El Niño
- During El Niño, the Northern Rainfall Onset (NRO) is likely to be delayed and there are usually fewer cyclones
- During La Niña, the NRO is likely to be early and there are more cyclones
- Central Pacific El Niño is when the sea surface temperatures are very warm in the central Pacific, near the dateline (180°) and are likely to have a greater impact on northern Australia