ENSO (El Niño Southern Oscillation)
The El Niño Southern Oscillation (ENSO) phenomenon describes the year-to-year variations in sea- surface temperatures across the equatorial Pacific Ocean. This affects atmospheric circulation and weather for many regions of the globe.
ENSO occurs in 3 phases as below:
- El Niño – warmer than average sea-surface temperatures in the Pacific Ocean
- La Niña – colder than average sea-surface temperatures in the Pacific Ocean
- Neutral or “La Nada” – sea-surface temperatures in the Pacific Ocean are close to average, these periods are often in transition between El Niño and La Niña events
ENSO typically affects weather in Southern Africa as below:
- El Niño – drier than average, lower rainfall
- La Niña – wetter than average, higher rainfall
- Neutral or “La Nada” – can be either or average, no distinct rainfall pattern
The “skill” or reliability of a seasonal forecast also varies according to which ENSO phase is in force during the current rainfall season. In general for Southern Africa, seasonal forecasts for conditions of both El Nino and La Nina can have relatively good skill, meaning that they are more likely to come true. Under Neutral conditions, however, the skill of the forecast is low, which means that one should not put much trust in such forecasts.
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