Beyond Stokes drift -- Lagrangian transport in evolving gravity waves

TL;DR

This paper investigates how evolving gravity waves affect particle transport, revealing that wave decay introduces new drift components and vertical transport, impacting mixing and surface transport modeling.

Contribution

It provides a combined simulation and analytical study of Lagrangian transport in decaying gravity waves, extending understanding beyond steady wave assumptions.

Findings

Wave decay introduces first- and second-order corrections to classical drift.

Decaying waves generate net vertical transport influenced by inertia and viscosity.

Transport effects alter particle trajectories and enhance anisotropic mixing.

Abstract

Finite-amplitude gravity waves at the air-water interface induce net fluid and particle transport, known as Stokes drift. While this mechanism is well understood for steady waves, transport under unsteady, evolving conditions remains poorly characterized. Here, we investigate Lagrangian transport in freely decaying waves using high-resolution two-phase simulations and a perturbative analytical model. Wave decay modifies the classical Lagrangian drift by introducing both first- and second-order corrections in the wave amplitude expansion, and generates a net vertical transport, governed by the balance between inertia and viscosity. These effects alter particle trajectories and enhance anisotropic mixing, with implications for interpreting field observations and modeling surface transport processes.