Impacts of the Combined Effect of ENSO Regimes and MJO on Daily Precipitation over the Amazon Basin: A Focus on Southern Peruvian Highland

The Madden–Julian Oscillation (MJO) and El Niño-Southern Oscillation (ENSO) cause extreme rainfall events over Amazon Basin on intraseasonal and interannual time scales. However, the physical mechanisms and predictability associated with the combined effect of the MJO and El ENSO regimes on daily precipitation in the Amazon Basin, with a focus on southern Peruvian highland, have been received few attentions. To assess that, we use different daily precipitation gridded and SST indices for ENSO regimes for the October–April season between 1980 and 2009. This study analyses the MJO influence on intraseasonal through a composite analysis and observed case study of the combinations of ENSO and MJO phases. Moderate and strong episodes of El Niño and La Niña are considered separately in this study as well as two different MJO indices (Multivariate- and convective-based MJO index).

Our results show that most of the dry extreme events occurred during El Niño years (moderate and strong), while wet extreme events are more recurrent during moderate La Niña or neutral years. Besides, the MJO convection could enhance or weaken the basic response of ENSO on extreme precipitation events. Indeed, some differences in the MJO impacts on intraseasonal precipitation by different MJO indices are noticed. On the other hand, especially over southern Peruvian highland, extratropical wave disturbances appear to play an important role in modulating precipitation.

The results also permit the identification of several sub monthly-to-intraseasonal scale potential predictors that modulate the occurrence of circulation regimes conducive to extreme rainfall events in the Amazon Basin and southern Peruvian highland.

Keywords: Intraseasonal rainfall variability, extreme precipitation, Amazon Basin, southern Peruvian highland, MJO, ENSO regimes