El Niño-Southern Oscillation is the most prominent modulator of atmospheric variability, and the major driver of climate teleconnections worldwide. It is certainly predictable, but state-of-the-art coupled models seem to have reached a plateau at moderate predictability level. Understanding the theoretical nature and activation mechanism of the phenomenon would ultimately enlarge its predictability, and in turn, improve seasonal forecasting worldwide. The present project will study the main mechanisms favoring the initial activation of El Niño (EN) events in the tropical Pacific, as well as those processes that explain the subsequent amplification and teleconnections of the phenomenon. The project will analyze these ocean-atmosphere interactions between the tropics and extratropics in observational datasets, and conclusions will be used for the validation of a large ensemble of timely state-of-the-art coupled climate models. The most skilful of these model schemes will be used for the design of new numerical experiments, which will shed further light on the main dynamical mechanisms explaining the generation of EN events. During this exhaustive study, the main leading processes and features will be identified, and used for the design of new operational statistical prediction schemes. In this way, the present project proposes to enlarge the predictability of the phenomenon by means of a comprehensive theoretical and practical study of the main leading mechanisms taking place during onset of EN events. Despite the present project is especially designed for increasing the professional maturity of the applicant as an independent researcher, it is also thought to improve the research attractiveness of the return host institution by transferring outstanding scientific expertise of a top international outgoing host institution to the return host center within the European Union.