A Two‐Part Model for Wave‐Sea Ice Interaction: Attenuation and Break‐Up.

Waves and sea ice form a closely coupled system: waves govern sea ice through stress, floe break‐up, and wave‐induced currents, while sea ice affects waves through attenuation and reflection. Wave‐induced sea ice break‐up is particularly important as it can regulate air‐sea interaction and consequently also regulate the growth and melt of sea ice. This coupled nature is complex and generally, especially at the large scale, neglected in modeling of the polar climate system. Here, we explore a novel way of coupling through wave‐induced ice break‐up, and conduct a case study for the Antarctic summer of 2019/2020. Our modeling approach builds upon previous investigations as follows: (a) sea ice takes a binary form, either "broken" or "unbroken," (b) waves may break sea ice, transitioning it from unbroken to broken, (c) a threshold separating breaking and nonbreaking wave fields is used to identify when this occurs, (c) two modes of attenuation for waves in ice (dependent upon the ice state), representing the observed on/off switch in wave attenuation. By characterizing wave attenuation and sea ice break‐up as described above, we achieve two‐way wave‐sea ice coupling, thereby allowing wave‐sea ice feedbacks. This model is limited to the ice‐melt season as refreeze is not represented here. We demonstrate that our model can simulate both the wavefield in and the evolution of the Marginal Ice Zone. Our results show the validity of empirically derived wave‐induced sea ice break‐up threshold, and substantiate that waves have a critical influence on the morphology of the Marginal Ice Zone. Plain Language Summary: The interactions between waves and sea ice are complex and, when represented in numerical models, often over‐simplified or even neglected. For example, waves act very differently in regions covered by small ice floes or broken ice compared to those covered by an unbroken cover of very large ice floes. Wave dissipation can differ by orders of magnitude, but wave‐forecast models usually try to find some "effective" parameters for their attenuation modules valid on average in both environments. Even more, sufficiently large waves can break the ice, thereby changing the behavior of waves in this region. Sea ice forms a crucial barrier between air and sea, and understanding when and how it breaks is crucial to understanding polar regions. Here, we introduce and test a simple yet effective model of wave‐ice interaction. Our results show that waves have a critical influence on evolution of sea ice, and are essential to understanding polar regions. Key Points: A new model of wave‐sea ice interaction, with coupling achieved through wave‐induced sea ice break‐up based on a nondimensional thresholdThe model is able to capture the position of the unbroken sea ice front and individual break‐up eventsThe ability of this simple wave model indicates that waves may have a critical influence on Marginal Ice Zone morphology [ABSTRACT FROM AUTHOR]