Influences of IOD and ENSO to Indonesian Rainfall Variability: Role of Atmosphere-ocean Interaction in the Indo-pacific Sector

The relative influences of Indian Ocean dipole (IOD) and El Niño–Southern Oscillation (ENSO) on Indonesian rainfall are investigated for seasonal time scales. For the period 1960–2011, observation and reanalysis products during September to November (SON) are used to assess the impacts of ENSO and IOD in Indonesian region. Composite of SSTs and Indonesian rainfall anomalies shows detailed features in the different phases of ENSO and IOD. A distinct impact on rainfall anomalies is found during the years when an El Niño and a positive IOD event or a La Nina and a negative IOD event co-occur indicating the interplay of ENSO and IOD in generating rainfall anomalies in Indonesian region. The atmospheric circulation and sea surface temperatures associated with these responses are discussed. Using composite analysis of anomalies of rainfall, sea surface temperature (SSTs), and circulation at any atmospheric levels, it is shown that positive anomalies of rainfall over Indonesia start to be decreased when SSTs surrounding Indonesia are cool and The Walker Circulation is weakened, resulting in anomalous surface easterlies across Indonesia. The composite analysis of rainfall anomalies and the SSTs showed that rainfall variability in Indonesia is clearly influenced by IOD and ENSO phenomena. This study highlights the atmosphere–ocean interaction in Indo-Pacific sector which plays an important role on Indonesian rainfall variability.