Topographic Modulation of Multisource Internal Solitary Waves in a Complex Sea Basin: Nonlinear Dynamics and Energetics

Abstract Complex basin topography plays a fundamental role in modulating the dynamics and energetics of internal solitary waves (ISWs), yet their three-dimensional mechanisms remain poorly understood. Here, a high-resolution nonhydrostatic numerical model is employed to investigate basin topographic modulations of the generation, nonlinear evolution, and energetics of multisource ISWs in the Sulu Sea basin. The model results show that both source region topography and propagation pathways jointly control the nonlinear evolution of ISWs. Specifically, western ISWs (ISW-W), generated over the sill through a lee-wave mechanism during transitions from supercritical to subcritical flow, exhibit strong initial nonlinearity. As they propagate into the deep basin, dispersion dominates, whereas nonlinear steepening is reintensified during shoaling. In contrast, eastern ISWs (ISW-E), generated at the shelf break via internal tide releasing mechanism, propagate primarily as linear internal tides across the basin and evolve into nonlinear wave trains only upon reaching the northern continental slope. Complex basin geometry induces spatial asymmetry in ISW energetics, manifested in both along-crest and propagation directions. The total energy of ISW-W is approximately twice that of ISW-E, reflecting differences in generation efficiency and energy transfer regulated by basin-scale topography. These results underscore the critical role of basin topography in shaping ISW dynamics and energetics in marginal seas.