Cumulative oceanic response to sequential tropical cyclones in the northern South China Sea

Tropical cyclones (TCs) induce strong oceanic responses that in turn modulate air-sea heat exchange and subsequent TC development, yet the cumulative impacts of multiple sequential TCs are insufficiently explored. This study investigates the ocean response to four sequential TCs in the northern South China Sea (SCS), emphasizing the interaction between TC forcing and pre-existing ocean thermal conditions. Using satellite observations and reanalysis data, we show that the successive TCs generated a distinct dual-core cooling structure in the surface and subsurface layers, accompanied by mixed layer deepening and barrier layer thickening. The oceanic response was jointly modulated by atmospheric environmental conditions, wind-driven vertical mixing, Ekman pumping, and surface heat flux exchange, with mesoscale eddies further adjusting its amplitude. The evolving upper-ocean state progressively reduced thermal favorability for intensification resulting in a stepwise weakening of the sequential TCs. These findings highlight the critical role of cumulative ocean preconditioning in modulating both ocean responses and TC intensity evolution, with implications for improving intensity prediction in regions prone to rapid cyclone succession.