Influence of ENSO and MJO Phases on Extreme Events of Precipitation over Amazon

Abstract:

Several droughts and floods in Amazonia has occurred in the last years - some of them being classified as the most severe in the last 40 years - and future projections from Intergovernmental Panel on Climate Change (IPCC) indicate an increase of these extreme events. El Niño Southern Oscillation (ENSO) is one of the phenomena associated with extreme rainfall events in the Amazon. However, some recent studies have indicated that the basic response of ENSO is dependent on the phase of the Madden-Julian Oscillation (MJO). Hence, this study aims to analyze the influence of the MJO on the extreme events over northern South America, and especially over Amazon, in El Niño and La Niña years. We intend to explore the relative importance of the MJO to precipitation anomalies during ENSO events. Extreme events of precipitation over northern South America for the austral summer (November to March) were obtained through a composite analysis of the combinations of ENSO and MJO phases. The results showed that the MJO convection can enhance or weaken the basic response of ENSO on extreme precipitation events. Moreover, the results show that during positive extreme rainfall events (floods) over Amazon there is also an enhancement of the precipitation over the South Atlantic Convergence Zone (SACZ) when the MJO is active (inactive) in El Niño (La Niña) years. Air circulation at high levels were also analyzed and supports these patterns. Therefore, they suggest that the influence of ENSO may be modulate by the MJO phase. This work contributes to a better understanding of the climate variability and will be helpful for the forecast of ENSO effects on extreme events of temperature and precipitation over South America. Also, this study presents preliminary results of one of the Collaborative Researches in Support of GOAmazon Campaign Science, funding by U.S. Department of Energy (DoE) and São Paulo Research Foundation (FAPESP).