Atlantic Zonal Mode: An Emerging Source of Indian Summer Monsoon Variability in a Warming World

Atlantic Zonal Mode (AZM) and Indian summer monsoon rainfall (ISMR) are known to have an inverse relationship, which means that the cold (warm) phases of AZM result in strong (weak) ISMR. Here, we report that the inverse relationship between AZM and ISMR has significantly strengthened in recent decades. The cause of this strengthening relationship has been investigated. We find a robust increase in interannual variability of sea surface temperature over the eastern tropical Atlantic Ocean in recent decades, which implies an increase in the number of strong AZM events toward the end of the twentieth century. The increase in strong AZM events alters the large-scale monsoon circulation over the Indian subcontinent by enhancing the Kelvin wave response into the Indian Ocean, leading to an enhanced AZM-ISMR teleconnection. This demands a better representation of the AZM-ISMR teleconnection in climate models for improving seasonal monsoon prediction in a warming world.