WIFF1.0: A hybrid machine-learning-based parameterization of Wave-Induced sea-ice Floe Fracture

Horvat, Christopher; Roach, Lettie A.

doi:10.5194/gmd-2021-281

Cited by 7 publications

(10 citation statements)

References 30 publications

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“…The sea ice and wave models are on a displaced-pole nominal 1∘ grid (gx1v7), and the size of model grid cells near observations in the Beaufort Sea is approximately 50 km×50 km. This model is the same as FSD-WAVEv2 in [3], except that (i) we use a higher wave-ice coupling frequency, exchanging the wave spectrum and SIC, thickness, and mean floe size every hour to better resolve short-time-scale wave-ice interactions; (ii) we modify the numerical approach such that the source term for wave-ice interactions in WW3, Sice, is applied alongside the other source terms without time-splitting (which appears to be impactful for the nominal 1∘ resolution); and (iii) we use WIFF1.0 [34] for floe fracture, which is a computationally efficient version of the parametrization in [33] developed using machine learning. In WW3, the global timestep is set to 1800 s, the spatial propagation is set to 600 s, the intra-spectral propagation is set to 1800 s, and the minimum source-term step is set to 20 s. The model spin-up period covers 2000–2018, and sensitivity experiments with varied attenuation schemes are run for one year each, branched from the spin-up at 1 January 2018.…”

Section: Methodsmentioning

confidence: 99%

Wind waves in sea ice of the western Arctic and a global coupled wave-ice model

Cooper

Roach

Thomson

et al. 2022

Phil. Trans. R. Soc. A.

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The retreat of Arctic sea ice is enabling increased ocean wave activity at the sea ice edge, yet the interactions between surface waves and sea ice are not fully understood. Here, we examine in situ observations of wave spectra spanning 2012–2021 in the western Arctic marginal ice zone (MIZ). Swells exceeding 30 cm are rarely observed beyond 100 km inside the MIZ. However, local wind waves are observed in patches of open water amid partial ice cover during the summer. These local waves remain fetch-limited between ice floes with heights less than 1 m. To investigate these waves at climate scales, we conduct experiments varying wave attenuation and generation in ice with a global model including coupled interactions between waves and sea ice. A weak high-frequency attenuation rate is required to simulate the local waves in observations. The choices of attenuation scheme and wind input in ice have a remarkable impact on the extent of wave activity across ice-covered oceans, particularly in the Antarctic. As well as demonstrating the need for stronger constraints on wave attenuation, our results suggest that further attention should be directed towards locally generated wind waves and their role in sea ice evolution. This article is part of the theme issue ‘Theory, modelling and observations of marginal ice zone dynamics: multidisciplinary perspectives and outlooks’.

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Section: Methodsmentioning

confidence: 99%

Wind waves in sea ice of the western Arctic and a global coupled wave-ice model

Cooper

Roach

Thomson

et al. 2022

Phil. Trans. R. Soc. A.

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“…W. Bateson et al: Impacts of floe size on sea ice mass elling techniques could significantly mitigate the computational cost (e.g. Horvat and Roach, 2022).…”

Section: Discussionmentioning

confidence: 99%

“…It is worth noting that future advancements in modelling techniques may reduce or mitigate the computational expense or complexity of either model; e.g. Horvat and Roach (2022) presented a machine-learning-based parameterisation to simulate wave break-up of sea ice floes that can replace the existing treatment of wave break-up in the prognostic model. The study found that CICE simulations including the prognostic model with this new parameterisation have an approximately 40 % longer run time than CICE simulations without the prognostic model, i.e.…”

Section: Advantages and Disadvantages Of Fsd Modelsmentioning

confidence: 99%

Sea ice floe size: its impact on pan-Arctic and local ice mass and required model complexity

et al. 2022

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Abstract. Sea ice is composed of discrete units called floes. Observations show that these floes can adopt a range of sizes spanning orders of magnitude, from metres to tens of kilometres. Floe size impacts the nature and magnitude of interactions between the sea ice, ocean, and atmosphere including lateral melt rate and momentum and heat exchange. However, large-scale geophysical sea ice models employ a continuum approach and traditionally either assume floes adopt a constant size or do not include an explicit treatment of floe size. In this study we apply novel observations to analyse two alternative approaches to modelling a floe size distribution (FSD) within the state-of-the-art CICE sea ice model. The first model considered is a prognostic floe size–thickness distribution where the shape of the distribution is an emergent feature of the model and is not assumed a priori. The second model considered, the WIPoFSD (Waves-in-Ice module and Power law Floe Size Distribution) model, assumes floe size follows a power law with a constant exponent. We introduce a parameterisation motivated by idealised models of in-plane brittle fracture to the prognostic model and demonstrate that the inclusion of this scheme enables the prognostic model to achieve a reasonable match against the novel observations for mid-sized floes (100 m–2 km). While neither FSD model results in a significant improvement in the ability of CICE to simulate pan-Arctic metrics in a stand-alone sea ice configuration, larger impacts can be seen over regional scales in sea ice concentration and thickness. We find that the prognostic model particularly enhances sea ice melt in the early melt season, whereas for the WIPoFSD model this melt increase occurs primarily during the late melt season. We then show that these differences between the two FSD models can be explained by considering the effective floe size, a metric used to characterise a given FSD. Finally, we discuss the advantages and disadvantages to these different approaches to modelling the FSD. We note that although the WIPoFSD model is unable to represent potentially important features of annual FSD evolution seen with the prognostic model, it is less computationally expensive and produces a better fit to novel FSD observations derived from 2 m resolution MEDEA imagery, possibly making this a stronger candidate for inclusion in climate models.

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“…For example, a 2019 storm in the Barents Sea was observed to generate waves in sea ice with heights above 2 m, which decayed over distances of several hundred kilometres into the sea ice near Svalbard (Horvat et al, 2020). With IS-2 operational since October 2018 and orbiting the Earth 15 times per day, the IS-2 dataset provides global coverage and combined with information about along-track floe sizes, concentrations and thicknesses can provide unique information about wave attenuation for climate models (Tilling et al, 2018;Horvat et al, 2019;Roach et al, 2019;Horvat and Roach, 2022).…”

Section: Introductionmentioning

confidence: 99%

Altimetric observation of wave attenuation through the Antarctic marginal ice zone using ICESat-2

et al. 2022

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Abstract. The Antarctic marginal ice zone (MIZ) is a highly dynamic region where sea ice interacts with ocean surface waves generated in ice-free areas of the Southern Ocean. Improved large-scale (satellite-based) estimates of MIZ extent and variability are crucial for understanding atmosphere–ice–ocean interactions and biological processes and detection of change therein. Legacy methods for defining the MIZ are typically based on sea ice concentration thresholds and do not directly relate to the fundamental physical processes driving MIZ variability. To address this, new techniques have been developed to measure the spatial extent of significant wave height attenuation in sea ice from variations in Ice, Cloud and land Elevation Satellite-2 (ICESat-2) surface heights. The poleward wave penetration limit (boundary) is defined as the location where significant wave height attenuation equals the estimated error in significant wave height. Extensive automated and manual acceptance/rejection criteria are employed to ensure confidence in along-track wave penetration width estimates due to significant cloud contamination of ICESat-2 data or where wave attenuation is not observed. Analysis of 304 ICESat-2 tracks retrieved from four months of 2019 (February, May, September and December) reveals that sea-ice-concentration-derived MIZ width estimates are far narrower (by a factor of ∼ 7 on average) than those from the new technique presented here. These results suggest that indirect methods of MIZ estimation based on sea ice concentration are insufficient for representing physical processes that define the MIZ. Improved large-scale measurements of wave attenuation in the MIZ will play an important role in increasing our understanding of this complex sea ice zone.

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WIFF1.0: A hybrid machine-learning-based parameterization of Wave-Induced sea-ice Floe Fracture

Cited by 7 publications

References 30 publications

Wind waves in sea ice of the western Arctic and a global coupled wave-ice model

Wind waves in sea ice of the western Arctic and a global coupled wave-ice model

Sea ice floe size: its impact on pan-Arctic and local ice mass and required model complexity

Altimetric observation of wave attenuation through the Antarctic marginal ice zone using ICESat-2

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