Long‐Term Strengthening of the Summer Indian Ocean Subtropical Cell and Its Underlying Mechanisms

Abstract The Indian Ocean Subtropical Cell (STC) is a shallow overturning circulation that links the subtropical and equatorial oceans and plays a key role in redistributing heat. Although strongest during boreal summer, its long‐term evolution remains poorly understood. Using multiple ocean reanalysis and pacemaker experiments, we show that the summer STC has significantly strengthened since 1980 (−0.047 ± 0.010 Sv yr −1 ). The experiments identify enhanced subtropical easterlies over the southern Indian Ocean, driven by the non‐uniform warming of the Indo‐Pacific warm pool, as an important contributor. The strengthened easterlies reinforce the STC by enhancing surface Ekman transport, promoting the subduction of subtropical waters into the thermocline, and strengthening subsurface geostrophic transport. These findings reveal how Indo‐Pacific warm‐pool warming reshapes tropical overturning circulation and improves our understanding of the oceanic response to global warming.