May 27, 2013 — El Niño wreaks havoc across the globe, shifting weather patterns that spawn droughts in some regions and floods in others. The impacts of this tropical Pacific climate phenomenon are well known and documented. A mystery, however, has remained despite decades of research: Why does El Niño always peak around Christmas and end quickly by February to April? Now there is an answer: An unusual wind pattern that straddles the equatorial Pacific during strong El Niño events and swings back and forth with a period of 15 months explains El Niño's close ties to the annual cycle.
http://www.sciencedaily.com/releases/2013/05/130527100628.htm