Zonal winds in the central equatorial pacific and el nino.

Easterly trade winds from near-equatorial islands in the central Pacific weakened before each El Niño between 1950 and 1978, except for the 1963 El Niño. The weakening of the easterlies and their later collapse did not occur uniformly over several months, but rather through a series of strong westerly wind bursts lasting 1 to 3 weeks. The bursts may force equatorial Kelvin waves in the ocean that can both initiate and sustain the sea surface warming characteristics of El Niño events.