| Abstract: |
| The ocean surface is intrinsically nonlinear, with resonant wave-wave interactions continuously shaping the wave field. As waves shoal toward the coast, dispersive effects weaken while nonlinearities become more strongly expressed. In this regime, weak-to-moderate amplitude modulation, spanning timescales from seconds to minutes, is readily observed in both Lagrangian and Eulerian measurements of the surface elevation. The transport of inertial particles within such wave fields remains a significant open problem in many disciplines. In this talk, we examine inertial particle trajectories under weakly modulated wave conditions representative of the nearshore zone. The dynamics reveal a clear two-scale structure: particles undergo oscillatory spiral motion at the carrier-wave frequency while simultaneously experiencing a slow back-and-forth drift governed by the group modulation. The amplitude, period, and net displacement of this drift depend sensitively on the modulation parameters and initial conditions. These findings reveal how the nonlinear group structure of nearshore waves regulates particle transport in ways not captured by current models, with direct implications for sediment transport, pollutant dispersion, and a more reliable assessment of the fate of buoyant material along coastlines. |
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