Advances in Geosciences www.adv-geosci.net 1680-7340 1680-7359 6 1st Alexander von Humboldt International Conference 2006 10.5194/adgeo-6-3-2006 http://www.adv-geosci.net/6/3/2006/ http://www.adv-geosci.net/6/3/2006/adgeo-6-3-2006.html http://www.adv-geosci.net/6/3/2006/adgeo-6-3-2006.pdf 3 15 2006-01-09 The ENSO phenomenon: theory and mechanisms H. A. Dijkstra Institute for Marine and Atmospheric Research, Dept. of Physics and Astronomy, Utrecht University, The Netherlands The variability in the equatorial Tropical Pacific is characterized by sea-surface temperature anomalies and associated changes in the atmospheric circulation. Through an enormous monitoring effort over the last decades, the relevant time scales and spatial patterns are fairly well-documented. In the meantime, a hierarchy of models has been developed to understand the physics of this phenomenon and to make predictions of future variability. In this short review, I try to summarize theories and mechanisms about variability in such a way that these are accessible to a diverse group of researchers, such as that present in Guayaquil (in May 2005) at the First International Alexander Von Humboldt Conference "The El Niño Phenomenon and its Global Impact".