El Niño - Southern Oscillation is an atmospheric-oceanic phenomenon that occurs in the tropical Pacific and is a powerful generator of climate variability on Earth. This graduate thesis explores its impact on the Indian Ocean, with an emphasis on precipitation. Meteorological fields were simulated using the numerical model SPEEDY, and for the sake of greater reliability of the results an ensemble analysis was made. An analysis of the empirical orthogonal functions was also performed, which gave a better insight into the significance of the obtained results of the connection between ENSO and precipitation over the Indian Ocean. Three diferent experiments were analysed, each one a result of an ensemble analysis of 35 numerical simulations differing in the forcing length in the tropical Pacific. The experiments were defined such that CTL represents a control experiment with forcing at the lower boundary via surface sea temperatures (SST) throughout the simulation. The JFM experiment has the same forcing at the lower boundary via the SST, but only during the winter (January to March), whereas in the ONDJFM experiment it has a longer duration (from October to March). The experiments thus defined have made it possible to study the effect of the length of the SST forcing during winter ENSO events on atmospheric events in the Indian Ocean. The results of this paper shown that the impact ENSO has on the precipitation in the Indian Ocean is not a simple function of the forcing length, but rather is a consequence of the complex processes of the interaction between the atmosphere and the sea. These include the direct ffect of the ENSO (via atmospheric processes) and the indirect (time-lengthened) ffect by generating SST anomalies in the Indian Ocean. Analysis using EOF showed that some of the variability of precipitation in the Indian Ocean area can be attributed to the impact of winter ENSO activity, which is especially pronounced in winter precipitation anomalies.