Influence of Madden-Julian Oscillation on Extreme Rainfall in Indonesia

This study investigates the influence of the Madden-Julian Oscillation (MJO) on extreme rainfall in different regions across Indonesia. The changes of probability of extreme events has been analyzed using TRMM satellite-derived rainfall data for wet (October-April) and dry (May-September) seasons and compared contemporaneously for eight MJO phases derived from the real time multivariate MJO index. The results show that during phase 2-4 (6-8) of MJO, MJO increase (decrease) the probability of extreme rainfall by about 80-150% (40-60%) during wet season 50-120% (40-60%) during dry season. Further investigation shows that the magnitude and timing of the impacts may vary in different regions in Indonesia; for instance, the western part of Indonesia experiences increase (decrease) of extreme rainfall probability on phase 2-4 (6-8) of the MJO by about 60-80% (20-60%) during wet season and 60-120% (50-60%) during dry season; whereas, the eastern part of Indonesia experiences increase (decrease) of extreme rainfall probability on phase 4-5 (7-1) of the MJO by about 60-80% (40-50%) during wet season and 60-80% (30-50%) during dry season. The change of probability of extreme rainfall events is highly associated with anomalous lower to middle-level circulation due to MJO; for example, the occurrence of enhanced (suppressed) rainfall extreme appears to result from induced upward (downward) motion of moisture and large-scale convective system; also, the timing of the impact is closely related to anomalous vertical moisture advection due to MJO. The results highlight the apparent MJO impact on extreme rainfall, along with its magnitude and timing across Indonesian region.