A mechanism for generating ENSO decadal variability

A coupled ocean-atmosphere model of the Pacific basin is used to illustrate a mechanism by which El Nino and the Southern Oscillation (ENSO) may be modulated on decadal time scales. For reasonable choices of model parameters, solutions exhibit two types of oscillation, an ENSO-like interannual mode and a decadal one. The decadal mode affects the equatorial zone by means of an oceanic teleconnection that involves transport variations of the North Pacific Subtropical Cell. Since almost half of the cool, thermocline water that upwells in the eastern equatorial Pacific participates ill this cell, these variations significantly alter the extent of the cold tongue, and hence provide an efficient mechanism for modulating ENSO.