El Niño and La Niña are alternating hot and cold periods in the atmosphere and ocean of the Pacific, each lasting about six months. These effects are monitored by the ‘sea surface temperature anomaly’ – the deviation in the temperature of a certain region of the Pacific ocean from its average temperature. El Niño and La Niña are defined as a difference of more than 0.4 degrees centigrade that lasts at least five months. The ‘southern oscillation index’ – the difference in atmospheric pressure between certain points in the Pacific – is also closely linked to El Niño and La Niña.

Climatologists had previously noticed that adjacent El Niños and La Niñas had similar intensities. This prompted Douglass’ team to study these effects over a longer period, and they gathered measurements of the sea surface temperature anomaly and the southern oscillation index spanning more than 30 years.

The researchers showed for the first time that the intensities of both El Niños and La Niñas went through a cycle lasting about 15 years, which consisted of a large peak and two successively smaller peaks. Douglass – whose background is in condensed matter physics – and co-workers realised that this pattern very closely matched a so-called Landau-Lifshitz function, an equation that describes many damped resonant systems in physics.

The Landau-Lifshitz function predicted many features of the super-Niño event detected in the climate data, together with some that have not been seen yet. The physicists – who point out that they are not climate experts – believe that climatologists could use these results to establish the nature of the force that drives the oscillations, and to predict forthcoming El Niños and La Niñas.

Douglass and colleagues based their study on data collected up to July 2000, and initially estimated the error of their model to be between 30% and 50%. But they have been encouraged by more recent data collected while they were writing their research paper, which closely fits their original predictions.

The physicists became involved in the study of El Niño while they were investigating how changes in the output of the Sun affect the Earth's temperature. “The El Niño effects are ‘noise' that has to be removed,“ Douglass told PhysicsWeb. “What was understood about El Niño was not good enough for us so we advanced the understanding ourselves.”