Mode-2 nonlinear internal waves (NLIWs) can play an important role in mixing and transporting material, however, their generation and evolution remain less well-understood than their mode-1 counterparts. Field observations from a mooring in 330 m water on the Australian North West Shelf (NWS) revealed frequent occurrence of mode-2 NLIWs with leading wave amplitude of 23 ± 8 m, followed by a train of trailing waves, and a propagation direction of 54^o ± 12^o SE (inshore). While these mode-2 NLIWs arrived every 12 h - 12.4 h, they were not directly linked to the local tidal forcing. Furthermore, the amplitude of the leading waves increased when the background stratification shifted from a 2-layer to a 3-layer regime. We used a non-hydrostatic (NH) ocean model to understand the mode-2 generation and propagation process and its link to the background density stratification and forcing. We ran a series of 2-dimensional (2D) NH model runs driven by both remote internal tides (RITs) with a low-frequency phase modulation and local barotropic forcing. The 2D modeling demonstrated that non-phase-locked mode-1 RITs scattered energy to a high mode beam at the shelf break. The shoreward-propagating internal wave beams interacted resonantly with the double-pycnocline (3-layer) stratification (generated by the passage of TC Veronica) to ultimately generate mode-2 NLIWs in shallower water with depths of around 500 m. Using knowledge from these 2D simulations, we then ran a 3D NH model with phase-modulated RITs and the model results were in good agreement with the observations. The complex interaction between local tidal forcing, remote internal tide forcing, and density stratification, all affected the timing and occurrence of mode-2 NLIWs on this continental shelf.

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