Atmospheric and Climate Sciences, 2017, 7, 48-64 http://www.scirp.org/journal/acs ISSN Online: 2160-0422 ISSN Print: 2160-0414 DOI: 10.4236/acs.2017.71005 January 16, 2017 Historical Phase-Locked El Niño Episodes David H. Douglass 1 , Robert S. Knox 1 , Scott Curtis 2* , Benjamin S. Giese 3 , Sulagna Ray 4 1 Department of Physics and Astronomy, University of Rochester, Rochester, NY, USA 2 Department of Geography, Planning, and Environment, East Carolina University, Greenville, NC, USA 3 Department of Oceanography, Texas A&M University, College Station, TX, USA 4 Atmospheric and Ocean Sciences Program, Princeton University, Princeton, NJ, USA Abstract Using a newly reported Pacific sea surface temperature data set, we extend a prior study that assigned El Niño episodes to distinct sequences. Within these sequences the episodes are phase-locked to subharmonics of the annual solar irradiance cycle having two- or three-year periodicity. There are 40 El Niño episodes occurring since 1872, each found within one of eighteen such sequences. Our list includes all prev- iously reported events. Three El Niño episodes have already been observed in boreal winters of 2009, 2012 and 2015, illustrating a sequence of 3-year intervals that began in 2008. If the climate system remains in this state, the next El Niño is likely to occur in boreal winter of 2018. Keywords Climate, Climatology, Solar Forcing, Seasonal Effects, El Niño, Phase Locking 1. Introduction In a paper “El Niño occurrences in the past four and a half centuries,” Quinn, Neal and Mayolo [1] catalogue such events based upon published accounts of changes in wind, currents, physical damage, rainfall, flooding. They give the dates and magnitudes of about a hundred historic El Niño episodes. The present era of quantitative characteriza- tions of the El Niño/La Niña phenomena has led to studying changes in the sea surface temperature (SST) of the equatorial Pacific Ocean. Positive variations in SST are called El Niño episodes and negative variations are called La Niña episodes. Where in the tropical Pacific are the El Niño phenomena to be found? By finding the location in the tropical Pacific with the strongest correlation with related phenomena, Barnston, Chelliah and Goldenberg [2] determined that a particular sea surface tem- perature (SST) area (latitude: 5˚S to 5˚N; longitude: 120˚W to 170˚W) that overlaps previously defined Area3 and Area4 was best. This area, to be called A34, has an aver- How to cite this paper: Douglass, D.H., Knox, R.S., Curtis, S., Giese, B.S. and Ray, S. (2017) Historical Phase-Locked El Niño Episodes. Atmospheric and Climate Scien- ces, 7, 48-64. http://dx.doi.org/10.4236/acs.2017.71005 Received: December 21, 2016 Accepted: January 13, 2017 Published: January 16, 2017 Copyright © 2017 by authors and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access