Role of Westerly Wind Bursts in driving the multi-year negative Indian Ocean Dipole of 2021-2022

Abstract

The tropical Indian Ocean experienced an unprecedented multi-year negative Indian Ocean Dipole (NIOD) during 2021–2022, coinciding with the triple-dip La Niña. Observations during this period show unusually frequent and strong Westerly Wind Bursts (WWBs) over the equatorial Indian Ocean. Here, we examine the role of WWBs in modulating oceanic variability during this event using an ocean model forced with atmospheric reanalysis. A control simulation is compared with a sensitivity experiment in which WWB-related wind variability is suppressed through localized smoothing of equatorial zonal winds in the Indian Ocean. The results show that WWBs significantly enhance eastward equatorial currents and generate downwelling equatorial Kelvin waves that propagate across the basin. These processes deepen the thermocline and increase upper-ocean heat content in the eastern tropical Indian Ocean. When WWBs are suppressed, the simulations exhibit weaker eastward transport, a shallower thermocline, and reduced subsurface heat accumulation. The results highlight the importance of intraseasonal wind bursts in regulating equatorial ocean dynamics and suggest that the unusually frequent WWBs during 2021–2022 contributed to sustaining the multi-year NIOD through enhanced eastward heat redistribution.