Two conductors lead the same orchestra. One waves the baton quickly, and the music changes every few seconds. The second barely moves, yet his slow breathing sets the overall rhythm of the symphony. So it is in the Pacific: one part of the wind swiftly moves warm water, while the other slowly reshapes the entire ocean.
Previously, scientists saw only one wind. Now they have split it into two parts. The first part is divergent: it pushes water apart, and warm water quickly gathers near the coasts of South America. That is El Niño. The second part is rotational: it swirls the water like a spoon in a cup, acting very slowly. This slow part generates waves that travel across the ocean for 25–27 years.
When a slow wave reaches the ocean's center, it strengthens or weakens El Niño. Hence, some decades bring many strong El Niños, while others bring few. Now, knowing both winds, scientists can better predict when the next strong El Niño will arrive.
The first scientific mention of El Niño dates to 1892, but Peruvian fishermen knew of the warm current off their coast at Christmas since the 17th century and called it "the Christ child."
In Kim Stanley Robinson's novel "Forty Signs of Rain," climate scientists battle the consequences of abrupt changes in ocean currents reminiscent of El Niño regime shifts, which here are explained by slow modulation of stratification.