An orchestra without a conductor: the instruments set the rhythm themselves. That is how the climate of the Indian and Pacific Oceans works. The surface water temperature there oscillates not haphazardly but in several hidden rhythms, from fast seasonal ones to very slow multi-decadal ones. Previously, to hear one rhythm, you had to muffle all the others, and in doing so you could lose important details. The new mathematical method works like an attentive listener: it takes in the entire orchestra and separates the music into individual parts, discarding nothing in advance.
Using this method, scientists analyzed ocean surface temperature data from 1300 years of model simulations and 140 years of observations. They identified several rhythms. One is El Niño, a well-known climate cycle with a period of about 4 years. But the most surprising discovery is that the combination of El Niño with the annual cycle explains up to 35% of temperature variability in the eastern Indian Ocean, right where the Indian Ocean Dipole is usually defined. This means that the Indian Ocean Dipole may not be an independent rhythm but merely an echo of the interaction between El Niño and the annual cycle.
Another finding is a very slow rhythm called the western Pacific multi-decadal mode. Its individual events last about 65 years, which is longer than the entire era of satellite observations of the ocean. To hear such a rhythm, you need very long data records. Now that we know about these hidden rhythms, it becomes clearer why the climate in the region changes the way it does and how to better predict droughts and monsoons.
The western Pacific multi-decadal mode (WPMM) is so slow that individual events can last longer than the entire satellite record of the ocean. For example, in the CCSM4 model, one positive WPMM event lasted about 65 years.
The idea of hidden periodicities governing climate echoes Isaac Asimov's novel 'The End of Eternity', where mathematicians compute cyclic changes in reality to manage human history.