The influence of cold SST anomalies surrounding the Maritime Continent on the El Niño-Indian monsoon teleconnection

Indian Summer Monsoon (ISM) precipitation is known to be influenced by both the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). El Niño events often coincide with droughts in the ISM region, yet there is considerable variability in the ISM response, partially due to coincident IOD events. However, it is unclear how SST patterns associated with different El Niño types combine with IOD-related SST anomalies to produce the ISM response. Here we use an atmospheric general circulation model forced by combinations of regional SST anomalies in both Pacific and Indian Oceans during the developing phase of El Niño (i.e., the ISM season prior to peak ENSO SST anomalies) to identify interactions in the teleconnection pathways. We find that the responses combine in a strongly non-linear manner. Consistent with previous studies, we find that IOD events largely counteract the influence of ENSO events, but also that this interaction depends on the pattern and magnitude of SST anomalies in the Indian Ocean. The impact on the ISM depends substantially on the details of the SST gradients, especially in the vicinity of the Maritime Continent where relatively minor differences in the pattern of cold SSTs and associated gradients generate regional circulation patterns that interfere with the large-scale teleconnection pathways. When combined with cold IOD SST anomalies, the influence of Eastern Pacific El Niño events on the ISM is smaller than the influence of Central Pacific El Niño events. Small differences in SST patterns and associated gradients can have substantial impacts on ISM precipitation anomalies, which may contribute to the observed variability in the ISM response to ENSO events, and as such are worthy of further research.