Dynamics of internal solitary waves south of the Lombok Strait

Southward-propagating internal solitary waves (ISWs) in the Lombok Strait represent an important but previously undocumented pathway for internal tide energy transfer from the Indonesian Seas into the eastern Indian Ocean. Here we present the first direct observational and analytical study of these southward-propagating ISWs, integrating shipboard Acoustic Doppler Current Profiler (SADCP) measurements acquired in November 2013, Korteweg–de Vries (KdV) theoretical reconstruction, satellite Synthetic Aperture Radar (SAR) imagery, and biogeochemical observations. The observed ISWs consist of a rank-ordered packet consisting of four solitary waves with progressively decreasing amplitudes of mode-1 depression waves with maximum vertical displacements of 35–50 m, phase speeds of ∼2.8–2.9 m s -1 , and horizontal half-widths of ∼0.9–1.1 km. KdV-based energetics reveal that the waves are potential-energy dominated, with kinetic-to-available potential energy ratios of 0.57–0.75, and that the leading four waves transport a total energy density of ∼412 MJ m -1 . Accounting for the arc-shaped wave fronts, the estimated energy flux reaches 2.3–2.8 GW per tidal cycle, indicating that a substantial fraction of internal tide energy generated at the Nusa Penida sill is radiated southward into deep waters. Seasonal analysis of KdV coefficients derived from Hybrid Coordinate Ocean Model (HYCOM) output demonstrates a marked contrast between the dynamically stable offshore propagation environment and the strongly seasonally modulated generation region near the sill, where transitions between subcritical and near-critical flow regulate ISW release. Biophysical observations further show that ISW-induced vertical displacements uplift the subsurface chlorophyll maximum by ∼10 m, enhance depth-integrated chlorophyll, and intensify shear-driven instability and turbulent mixing within the thermocline. These results highlight the role of southward-propagating ISWs as efficient carriers of tidal energy and as episodic drivers of vertical mixing and biogeochemical fluxes in the southern Lombok Strait, underscoring their importance for regional energy budgets and ecosystem functioning in tropical straits.