Scientists from the University of Hawaii at Manoa’s Department of Meteorology and the International Pacific Research Center have solved a long-standing riddle concerning wind patterns associated with El Niño.

While scientists have compiled extensive research about the disruptive climate phenomenon, the answer to why El Niño peaks around Christmas and quickly ends between February and April remained elusive until the Hawaii scientists identified a link between an unusual wind pattern that straddles the equatorial Pacific during strong El Niño events and El Niño’s annual cycle.

According to the team’s findings, available in the May 26 online edition of Nature Geoscience, the atmospheric pattern peaks in February and triggers droughts, heavy rainfall and other telltale El Niño events. When tradewinds shift south, they can terminate an El Niño by triggering an upwelling of cold water in the eastern equatorial Pacific. This wind shift is part of the larger, unusual atmospheric pattern that accompanies El Niño events.

The scientists used numerical atmospheric models to trace the development of this unusual pattern to an interaction between El Niño and the seasonal evolution of temperatures in the western tropical Pacific warm pool.