WIce-FOAM 1.0: coupled dynamic and thermodynamic modelling of heterogeneous sea ice and waves using OpenFOAM-v2306

Abstract

We present WIce-FOAM 1.0, a numerical model built on OpenFOAM that couples the dynamics and thermodynamics of heterogeneous sea ice to analyse waves’ response in marginal ice zone regions composed of consolidated ice floes and interstitial grease ice. The model represents prototypical conditions on the 5 km scale, where each 10 m grid cell classified as ice floe or grease ice may contain both ice types, but are predominantly occupied by one. Our model aims to study the mean shear viscosity of heterogeneous sea ice to bridge the gap with larger-scale ocean-sea ice models in which sub-grid details and wave effects are neglected. We tested the model in the Southern Ocean using a realistic sea-ice field from a SAR satellite image and complemented our analysis by idealised simulations. The thermodynamic model was coupled online to optimize the stiffness of the process scales and to explicitly account for the distinct characteristics of different ice types. We first investigated the dynamic response of sea ice to one-way wave forcing across a range of wave periods and directions. The results show that the domain-averaged sea-ice viscosity is scale invariant from approximately 800 m to 5 km and is primarily governed by the relative proportion of ice floes to grease ice, with less sensitivity to wave periods and directions. While the wave direction affects the local strain rate and viscosity, and the presence and orientation of narrow connections between the larger ice floes significantly influence the mean viscosity, these effects do not break the observed scale invariance. Finally, we demonstrate that, despite the different time scales, the mean viscosity responds nonlinearly to the inclusion of thermodynamic sea-ice growth. This model represents a first step towards a mechanistic understanding and description of heterogeneous sea ice, which is common in the Antarctic and is increasing in the warming Arctic. It can be used to design field experiments and to derive parametrisations of waves-in-ice response for large-scale sea-ice models.