The tropics breathe with an annual rhythm: air temperature rises and falls, and within this breathing lie two main pulses. The first pulse is strong in February and weak in August; the second is shifted by half a year. These two pulses are not just a backdrop for the famous El Niño but its conductors.

Scientists decomposed the daily temperature variations into two main modes using eigenanalysis and introduced a measure called "microcorrelation" to track how the El Niño region is linked to the Northern and Southern Hemispheres. It turned out that before El Niño onset, the region suddenly locks onto the Northern Hemisphere, and at the end of the event it switches to the Southern Hemisphere. This is like a tug of war: first one side pulls harder, then the other.

Returning to the tropical breathing: the two pulses, once seen as mere seasonal noise, actually drive the planet's most famous climate seesaw. They can be used to improve seasonal forecasts of El Niño, especially in predicting the rapid decay of events.