Nonlinear simulation of wave group attenuation due to scattering in broken floe fields

TL;DR

This study uses nonlinear simulations to analyze how ocean waves are attenuated by scattering in fragmented sea ice, revealing frequency-dependent behaviors and the importance of nonlinear interactions, with results aligning with Arctic field observations.

Contribution

It introduces a nonlinear simulation framework for wave-ice interactions that captures complex scattering effects and explains the roll-over phenomenon observed in Arctic experiments.

Findings

Wave attenuation increases with frequency.

Non-monotonic attenuation near a specific frequency.

Nonlinear interactions are crucial for the roll-over effect.

Abstract

Direct phase-resolved simulations are performed to investigate the propagation and scattering of nonlinear ocean waves in fragmented sea ice. The numerical model solves the full time-dependent equations for nonlinear potential flow coupled with a nonlinear thin-plate representation of the ice cover, and neglects dissipative processes. The two-dimensional setting with incident wave groups on deep water is considered, in view of applications to wave attenuation along transects of the marginal ice zone. A spatially-varying weight is assigned to the surface pressure so that irregular distributions of ice floes can be directly specified in the physical domain. For various wave regimes and floe configurations, a local wave spectrum across the ice field is computed and then least-squares fitted to extract a spatial attenuation rate as a function of wave frequency. A general increase with frequency is found, consistent with typical predictions from linear theory. However, a non-monotonic behavior around a certain frequency is also observed, especially in cases with a highly fragmented ice cover. Comparison to field data shows that this result closely resembles the roll-over phenomenon as reported from Arctic Ocean experiments. The key role played by nonlinear interactions in the roll-over development is highlighted.