Impacts of the Boreal Summer Intraseasonal Oscillation on marine heatwaves in the Taiwan Strait

The Taiwan Strait is a hotspot for frequent and intense marine heatwaves (MHWs) in summer, with severe impacts on local marine ecosystems, yet their underlying mechanisms remain elusive. Recent studies have documented the drivers of MHWs from interannual timescales to long-term changes, while the role of intraseasonal variability is still underexplored. The Boreal Summer Intraseasonal Oscillation (BSISO) is a prominent component of the atmospheric intraseasonal oscillation (ISO) over the tropical Indo-Pacific Ocean. Here, we examine the modulation of BSISO on MHW features over the Taiwan Strait in June–August during 1993–2024, and explore the BSISO-associated local physical processes responsible for each regional MHW. Sea surface temperature and probability of MHW occurrence in the Taiwan Strait fluctuate as the BSISO convection propagates, with the most pronounced increase during phases 4 + 5. Statistical analysis reveals that 52% of regional MHWs coincide with these specific phases, with longer duration and greater cumulative intensity than other events. These regional MHWs are primarily induced by enhanced solar radiation under clear-sky conditions during BSISO phases 4 + 5. Composite heat budget results indicate that intraseasonal shortwave radiation changes contribute approximately 58% of the mixed layer warming tendency and facilitate the genesis and intensification of MHWs. The findings on the physical processes linking the BSISO to MHWs may provide insights into the mechanisms of MHWs from an intraseasonal perspective.