Influence of the MJO on Extreme Precipitation Events over the Eastern Pacific Ocean

The Madden-Julian Oscillation (MJO) is the main mode of intraseasonal variability over the tropics. We aim to explore the MJO modulation on extreme precipitation events by analyzing atmospheric variables from ERA5 and oceanic variables from the NOAA and HYCOM reanalysis over the Eastern Pacific Ocean from May to November during the 1982-2018 period. The Real-time Multivariate MJO Index (RMM) is used to define the MJO phases. Only strong MJO phases are considered for this study. During MJO phases 3-7, the Eastern Pacific Ocean warm pool goes through a large expansion, but rainfall decreases near the Mexican Pacific coast. On the other hand, MJO phases 8, 1, and 2 induce an increase in precipitation over the continental part of the Middle Americas, making extreme precipitation events more frequent, but these phases decrease the warm pool extension near the Pacific coast. Additionally, the MJO compounds are classified according to El Niño Southern Oscillation (ENSO) years. MJO phases under Neutral and El Niño years have similar patterns in the atmospheric variables. However, these patterns drastically change in MJO phases under La Niña years, as the warm pool expansion decreases and the decrease/increase in rainfall is more intense compared to Neutral and El Niño years. We also noticed that the warm pool expansion and extreme precipitation events do not occur simultaneously. There is a lag of 7 days, as previous studies found but for the Indian Ocean. We conclude that these results are important to understand the air-ocean coupling for MJO and its application for sub-seasonal forecasts.