Spectral wave energy dissipation due to under-ice turbulence

TL;DR

This paper introduces an improved spectral model for wave energy dissipation under sea ice, accounting for turbulence, ice concentration, and floe size, validated with observational data from a sea ice break-up event.

Contribution

It proposes a novel source term for spectral wave models that incorporates spectral effects, ice concentration, and floe size, based on discrete-element modeling and bottom friction analogies.

Findings

Attenuation curves and frequency dependence analyzed for compact ice.

Floe size influences attenuation intensity and spectral distribution.

Model calibrated successfully with observational data from sea ice break-up.

Abstract

Dissipation within the turbulent boundary layer under sea ice is one of many processes contributing to wave energy attenuation in ice-covered seas. Although recent observations suggest that the contribution of that process to the total energy dissipation is significant, its parameterizations used in spectral wave models are based on fairly crude, heuristic approximations. In this paper, an improved source term for the under-ice turbulent dissipation is proposed, taking into account the spectral nature of that process (as opposed to parameterizations based on the so-called representative wave), as well as effects related to sea ice concentration and floe-size distribution, formulated on the basis of the earlier results of discrete-element modeling. The core of the new source term is based on an analogous model for dissipation due to bottom friction derived by Weber in 1991 (https://doi.org/10.1017/S0022112091003634). The shape of the wave energy attenuation curves and frequency-dependence of the attenuation coefficients are analyzed in detail for compact sea ice. The role of floe size in modifying the attenuation intensity and spectral distribution is illustrated by calibrating the model to observational data from a sudden sea ice break-up event in the marginal ice zone.