Response of seasonal phase locking of Indian Ocean Dipole to global warming

The Indian Ocean Dipole (IOD) is one of the major climate modes in the tropical Indian Ocean (TIO), influencing the surrounding climate and society. Under anthropogenic warming, the IOD is modulated by the changes in the ocean-atmosphere coupling in the TIO. This study focuses on the IOD seasonal phase locking, which means that the IOD usually peaks in boreal autumn. Based on high-emission scenario future projections, we found that the IOD phase locking changes substantially under anthropogenic warming. The early onset positive IOD that peaks in boreal summer occurs more frequently in the future climate. Our further investigation reveals that this robust change in IOD phase locking is related to the mean state responses to global warming. The shallower thermocline in the eastern equatorial IO is more suitable for IOD developing, helping IOD strengthen in boreal summer When the basin-wide IOD pattern has fully developed, by contrast, the weakened atmospheric feedback is not conducive to maintaining zonal sea surface temperature gradient, leading to IOD weakened in boreal autumn. Therefore, the IOD peaks earlier under global warming. The change in IOD phase locking shows a potential impact on the surrounding climate, such as Indian summer monsoon variability.