This study examines the seasonal dynamics of deep-water overflow in the Luzon Strait (LS) through numerical simulations and observational analysis. Results highlight the critical interplay between upper and deeper layer processes that govern the overflow's seasonality. The primary driving force behind these dynamics is identified as the bottom along-isobath pressure gradient force (PGF_along) over the Bashi Channel and the Luzon Trough. Generally, both the upper layer (above 500 m) and deeper layer (below 2,000 m) of the LS positively contribute to the PGF_along and deep-water overflow. The upper PGF_along was influenced by water level difference crossing the strait, while the deep PGF_along was sustained by density difference between the Pacific Ocean and the South China Sea (SCS). In terms of seasonality, the intensity and pathway of the Kuroshio vary and impact surface sea levels accordingly. This triggered oscillations in the isopycnal surfaces, mainly transmitted to the PGF_along over the Bashi Channel. The oscillations from the surface, along with density oscillation signals from the deep Pacific Ocean, collectively regulated the variability of the deep-water overflow in the LS. The density oscillation from the deep SCS side generally played a minor role. Weakening in atmospheric conditions or reductions in upper-layer flux markedly decrease both the intensity and variability of this overflow, underscoring the interconnectedness of atmospheric influences and oceanic responses in this region.

Seasonal variability,Numerical simulation,Deep overflow,western Pacific