UNDERSTANDING EL NINO IN OCEAN-ATMOSPHERE GENERAL CIRCULATION MODELS Progress and Challenges

Determining how El Nino and its impacts may change over the next 10 to 100 years remains a difficult scientific challenge. Ocean-atmosphere coupled general circulation models (CGCMs) are routinely used both to analyze El Nino mechanisms and teleconnections and to predict its evolution on broad range of time scales, from seasonal to centennial. The ability to simulate El Nino as an emergent property of these models has largely improved over the last few years. Nevertheless, the diversity of model simulations of present-day El Nino indicates current limitations in our ability to model this climate phenomenon and to anticipate changes in its characteristics. A review of the several factors that contribute to this diversity, as well as potential means to improve the simulation of El Nino, is presented.