Predicting El Nino and La Nina

The 1997 El Niño observed by TOPEX/Poseidon

It may be a little stronger than the metaphorical flapping of a butterfly’s wings in Brazil causing a hurricane on the coast of Australia, but the localised Pacific Ocean climate pattern known as the El Niño-Southern Oscillation is associated with floods, droughts and other severe weather effects throughout the world, and affects the livelihoods of millions of people.

You may have heard of El Niño as a result of the complication it adds to global climate models. Resolving such modelling difficulties requires an accurate knowledge of local sea-surface temperatures and wind speeds, with which we can better predict El Niño and associated La Niña events. The problem is that advance warning has so far been limited by a predictability barrier which is the northern hemisphere spring.

According to Tokyo University climatologist Takeshi Izumo and others, that difficulty could be overcome with a better understanding of the Indian Ocean Dipole – an oceanographic phenomenon which leads to an oscillation in sea-surface temperatures roughly every other year between the western and eastern waters of the Indian Ocean. For example, the positive phase of the oscillation, with warmer waters in the west and a corresponding cooling in the eastern Indian Ocean, leads to droughts in Indonesia and Australia. Conversely, the negative phase, with warmer waters in the east, causes cooler and drier conditions in the west. In addition, the Indian Ocean Dipole has a major effect on monsoon rainfall over the Indian subcontinent.

The Indian Ocean Dipole is linked to the global climate, and interacts strongly with the El Niño-Southern Oscillation. In their Nature Geoscience paper, Izumo and colleagues show that the negative dipole phase tends to be followed by an El Niño event more than a year later, and the positive phase leads a La Niña event by a similar period. The proposed physical connection is based on rapid changes in sea surface wind speed in the Pacific following the decay of a dipole event in the Indian Ocean during the northern autumn or winter.

It is this link between the Indian Ocean Dipole and El Niño-Southern Oscillation which provides a bridge over the spring predictability barrier for El Niño events. A better understanding should come from detailed observations of the response of the Indian Ocean to monsoon wind patterns.

Further reading

Izumo et al., “Influence of the state of the Indian Ocean Dipole on the following year’s El Niño”, Nature Geoscience (2010)

Peter J Webster & Carlos D Hoyos, “Beyond the spring barrier?”, Nature Geoscience (2010)