El Niño Southern Oscillation connection

Abstract

The Madden-Julian Oscillation (MJO) is the most pronounced signal in tropical intraseasonal (20–90 days) variability, and the El Nino Southern Oscillation (ENSO) is the most dominant interannual climate phenomenon in the tropical ocean-atmosphere system. Both MJO and ENSO involve major shifts in tropical convection, large-scale circulation, and weather patterns around the world. The hypothesis that the MJO and ENSO may be intrinsically linked was first proposed in the mid-1980s by Lau (1985a, b). Subsequently, many observational and modeling studies have appeared in the literature debating the merits of the hypothesis. Today, while the MJO-ENSO connection is still a topic of active research (Zhang et al., 2001), knowledge gained from better understanding of the causes and evolution of the MJO and ENSO has been incorporated into long-range weather forecasting and climate prediction schemes, resulting in improved forecasts not only in the tropics but also in many extra-tropical regions. A key factor in the prediction improvement is the recognition that the MJO and ENSO events do not act independently, but may interact with each other to provide the long-term pre-conditions, and the short-term fine tuning needed for better skill in long-range (> months) predictions. How can the MJO and ENSO — two phenomena with widely separate timescales, be physically linked and interact with each other? This critical question and related issues will be addressed in this chapter.