Impact of El Nino and El Nino Modoki Events on Indonesian Rainfall

On an interannual time-scale, the Indonesian climate is strongly influenced by the dynamics of Indo-Pacific climate modes. This study aims to investigate the possible impact of different types of El Nino events, namely, typical El Nino and El Nino Modoki, on Indonesian rainfall variability. Seasonal composite analysis was used to evaluate the magnitude and significance level of the influence of El Nino on the rainfall variability over the Indonesian region. Typical El Nino (hereafter El Nino) has a stronger influence on Indonesian rainfall than the El Nino Modoki during boreal autumn in September, October, and November when the events almost reach their peak. Cold sea surface temperature (SST) anomalies were observed in the Indonesian sea and in the western Pacific during El Nino years, while cold SST anomalies covered only the eastern Indonesian sea during El Nino Modoki years. Strong cold SST anomalies during El Nino years led to stronger low-level wind divergence over the Maritime Continent compared with that during El Nino Modoki years. In addition, the Walker circulation during El Nino years revealed a stronger downward motion over the Maritime Continent than that observed during El Nino Modoki years. This stronger downward motion (low-level wind divergence) during El Nino years reduced lower atmospheric water vapor and suppressed atmospheric convection over the Maritime Continent, leading to a significant decrease in rainfall. Similar situations were also observed during El Nino Modoki years but with a much weaker amplitude.