Do coastal or equatorial wind anomalies drive the Indian Ocean Dipole?

Based on first scientific principles, this study shows that both equatorial and coastal wind anomalies influence the development of positive phases of the Indian Ocean Dipole (IOD) in the south-east tropical Indian Ocean (SETIO). While southeasterly winds are favorable for upwelling along Sumatra's southwest coast, zonal equatorial wind anomalies are the main control of IOD variability given that the resultant Kelvin wave enhances or suppresses the Sumatran upwelling. Many previous studies have argued that easterly equatorial wind anomalies in the SETIO are essential for triggering the positive Bjerknes feedback, and thereby, the development of positive IOD (pIOD) events. With a focus on the particularly strong pIOD event of 2019, here we show that pIOD events can also evolve in the absence of zonal equatorial wind anomalies. Hence, it is possible that the Bjerknes feedback along the equator is less involved in IOD variability than previously thought. • Explores the ocean's response to wind forcing in the eastern tropical Indian Ocean. • Zonal equatorial wind anomalies are the main control of IOD variability. • Positive IOD events can evolve in the absence of zonal equatorial wind anomalies.