Modal energy distribution and propagation characteristics of internal tides in the South China Sea and Luzon Strait

Based on numerical simulation and modal decomposition, this study investigates the spatial distribution and propagation characteristics of baroclinic kinetic energy (KE) associated with different modes of M2 and K1 internal tides in the Luzon Strait (LS) and the South China Sea (SCS). The regionally averaged baroclinic KE of the M2 internal tide generated in LS is approximately 10.0 kJ m−2, which is significantly higher than that of the K1 internal tide (∼5.1 kJ m−2). However, M2 energy dissipates more rapidly during propagation. In general, baroclinic KE decreases with increasing distance from the generation area. The K1 internal tide exhibits multi-source characteristics within the SCS, leading to anomalous energy distributions in certain areas. Mode-1 accounts for over 50% of the total baroclinic KE for both M2 and K1 internal tides, serving as the dominant component for long-distance propagation. Topographic interactions facilitate energy transfer from lower to higher modes, resulting in reduced energy decay of high modes and enhanced decay of low modes in regions far from the LS. This process may also contribute to the observed reduction in mode-1 of K1 energy near the generation area. Higher-mode internal tides, especially the fourth and fifth modes, dissipate rapidly near their generation area and thus propagate over shorter distances, primarily in the east–west direction. In contrast, lower-mode internal tides exhibit a gradual southward deflection in the propagation direction with increasing distance.