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Vernon A Squire - One of the best experts on this subject based on the ideXlab platform.

  • modelling wave induced sea Ice break up in the Marginal Ice Zone
    Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 2017
    Co-Authors: Fabien Montiel, Vernon A Squire
    Abstract:

    A model of Ice floe break-up under ocean wave forcing in the Marginal Ice Zone (MIZ) is proposed to investigate how floe size distribution (FSD) evolves under repeated wave break-up events. A three-dimensional linear model of ocean wave scattering by a finite array of compliant circular Ice floes is coupled to a flexural failure model, which breaks a floe into two floes provided the two-dimensional stress field satisfies a break-up criterion. A closed-feedback loop algorithm is devised, which (i) solves the wave-scattering problem for a given FSD under time-harmonic plane wave forcing, (ii) computes the stress field in all the floes, (iii) fractures the floes satisfying the break-up criterion, and (iv) generates an updated FSD, initializing the geometry for the next iteration of the loop. The FSD after 50 break-up events is unimodal and near normal, or bimodal, suggesting waves alone do not govern the power law observed in some field studies. Multiple scattering is found to enhance break-up for long waves and thin Ice, but to reduce break-up for short waves and thick Ice. A break-up front marches forward in the latter regime, as wave-induced fracture weakens the Ice cover, allowing waves to travel deeper into the MIZ.

  • modelling wave induced sea Ice breakup in the Marginal Ice Zone
    arXiv: Atmospheric and Oceanic Physics, 2017
    Co-Authors: Fabien Montiel, Vernon A Squire
    Abstract:

    A model of Ice floe breakup under ocean wave forcing in the Marginal Ice Zone (MIZ) is proposed to investigate how floe size distribution (FSD) evolves under repeated wave breakup events. A three-dimensional linear model of ocean wave scattering by a finite array of compliant circular Ice floes is coupled to a flexural failure model, which breaks a floe into two floes provided the two-dimensional stress field satisfies a breakup criterion. A closed-feedback loop algorithm is devised, which (i)~solves wave scattering problem for a given FSD under time-harmonic plane wave forcing, (ii)~computes the stress field in all the floes, (iii)~fractures the floes satisfying the breakup criterion and (iv)~generates an updated FSD, initialising the geometry for the next iteration of the loop.The FSD after 50 breakup events is uni-modal and near normal, or bi-modal. Multiple scattering is found to enhance breakup for long waves and thin Ice, but to reduce breakup for short waves and thick Ice. A breakup front marches forward in the latter regime, as wave-induced fracture weakens the Ice cover allowing waves to travel deeper into the MIZ.

  • attenuation and directional spreading of ocean wave spectra in the Marginal Ice Zone
    Journal of Fluid Mechanics, 2016
    Co-Authors: Fabien Montiel, Vernon A Squire, Luke G Bennetts
    Abstract:

    A theoretical model is used to study wave energy attenuation and directional spreading of ocean wave spectra in the Marginal Ice Zone (MIZ). The MIZ is constructed as an array of tens of thousands of compliant circular Ice floes, with randomly selected positions and radii determined by an empirical floe size distribution. Linear potential flow and thin elastic plate theories model the coupled water–Ice system. A new method is proposed to solve the time-harmonic multiple scattering problem under a multidirectional incident wave forcing with random phases. It provides a natural framework for tracking the evolution of the directional properties of a wave field through the MIZ. The attenuation and directional spreading are extracted from ensembles of the wave field with respect to realizations of the MIZ and incident forcing randomly generated from prescribed distributions. The averaging procedure is shown to converge rapidly so that only a small number of simulations need to be performed. Far-field approximations are investigated, allowing efficiency improvements with negligible loss of accuracy. A case study is conducted for a particular MIZ configuration. The observed exponential attenuation of wave energy through the MIZ is reproduced by the model, while the directional spread is found to grow linearly with distance. The directional spreading is shown to weaken when the wavelength becomes larger than the maximum floe size.

  • wave Ice interactions in the Marginal Ice Zone part 1 theoretical foundations
    Ocean Modelling, 2013
    Co-Authors: Timothy D Williams, Dany Dumont, Laurent Bertino, Luke G Bennetts, Vernon A Squire
    Abstract:

    Abstract A wave-Ice interaction model for the Marginal Ice Zone (MIZ) is reported that calculates the attenuation of ocean surface waves by sea Ice and the concomitant breaking of the Ice into smaller floes by the waves. Physical issues are highlighted that must be considered when Ice breakage and wave attenuation are embedded in a numerical wave model or an Ice/ocean model. The theoretical foundations of the model are introduced in this paper, forming the first of a two-part series. The wave spectrum is transported through the Ice-covered ocean according to the wave energy balance equation, which includes a term to parameterize the wave dissipation that arises from the presence of the Ice cover. The rate of attenuation is calculated using a thin-elastic-plate scattering model and a probabilistic approach is used to derive a breaking criterion in terms of the significant strain. This determines if the local wave field is sufficient to break the Ice cover. An estimate of the maximum allowable floe size when Ice breakage occurs is used as a parameter in a floe size distribution model, and the MIZ is defined in the model as the area of broken Ice cover. Key uncertainties in the model are discussed.

  • wave Ice interactions in the Marginal Ice Zone part 2 numerical implementation and sensitivity studies along 1d transects of the ocean surface
    Ocean Modelling, 2013
    Co-Authors: Timothy D Williams, Dany Dumont, Luke G Bennetts, Vernon A Squire, Laurent Bertino
    Abstract:

    The theoretical foundation of a wave–Ice interaction model is reported in Part 1 of this study. The model incorporates attenuation of ocean surface waves by sea Ice floes and the concomitant breaking of the floes by waves that determines the structure of the Marginal Ice Zone (MIZ). A numerical implementation of the method is presented here. Convergence of the numerical method is demonstrated, as temporal and spatial grids are refined. A semi-analytical method, which does not require time-stepping, is also developed to validate the numerical results, when dispersion is neglected. The wave energy lost during Ice breakage is parameterized, as part of the numerical method. Sensitivity studies are conducted in relation to the energy loss and also dispersive effects, the choIce of the attenuation model, the properties of the wave field, and sea Ice properties such as concentration, thickness and breaking strain. Example simulations intended to represent conditions in the Fram Strait in 2007, which exploit reanalyzed wave and Ice model data, are shown to conclude the results section. These are compared to estimates of MIZ widths based on a concentration criteria, and obtained from remotely-sensed passive microwave images.

Luke G Bennetts - One of the best experts on this subject based on the ideXlab platform.

  • drift of pancake Ice floes in the winter antarctic Marginal Ice Zone during polar cyclones
    arXiv: Atmospheric and Oceanic Physics, 2019
    Co-Authors: Alberto Alberello, Luke G Bennetts, Miguel Onorato, Marcello Vichi, Clare Eayrs, Keith Machutchon, Petra Heil, Alessandro Toffoli
    Abstract:

    High temporal resolution in--situ measurements of pancake Ice drift are presented, from a pair of buoys deployed on floes in the Antarctic Marginal Ice Zone during the winter sea Ice expansion, over nine days in which the region was impacted by four polar cyclones. Concomitant measurements of wave-in-Ice activity from the buoys is used to infer that pancake Ice conditions were maintained over at least the first seven days. Analysis of the data shows: (i)~unprecedentedly fast drift speeds in the Southern Ocean; (ii)~high correlation of drift velocities with the surface wind velocities, indicating absence of internal Ice stresses $>$100\,km in from the edge in 100\% remotely sensed Ice concentration; and (iii)~presence of a strong inertial signature with a 13\,h period. A Langrangian free drift model is developed, including a term for geostrophic currents that reproduces the 13\,h period signature in the Ice motion. The calibrated model is shown to provide accurate predictions of the Ice drift for up to 2\,days, and the calibrated parameters provide estimates of wind and ocean drag for pancake floes under storm conditions.

  • brief communication pancake Ice floe size distribution during the winter expansion of the antarctic Marginal Ice Zone
    The Cryosphere, 2019
    Co-Authors: Luke G Bennetts, Alberto Alberello, Miguel Onorato, Marcello Vichi, Clare Eayrs, Keith Machutchon, Alessandro Toffoli
    Abstract:

    Abstract. The size distribution of pancake Ice floes is calculated from images acquired during a voyage to the Antarctic Marginal Ice Zone in the winter expansion season. Results show that 50 % of the sea Ice area is made up of floes with diameters of 2.3–4 m. The floe size distribution shows two distinct slopes on either side of the 2.3–4 m range, neither of which conforms to a power law. Following a relevant recent study, it is conjectured that the growth of pancakes from frazil forms the distribution of small floes ( D  m), and welding of pancakes forms the distribution of large floes ( D>4  m).

  • attenuation and directional spreading of ocean wave spectra in the Marginal Ice Zone
    Journal of Fluid Mechanics, 2016
    Co-Authors: Fabien Montiel, Vernon A Squire, Luke G Bennetts
    Abstract:

    A theoretical model is used to study wave energy attenuation and directional spreading of ocean wave spectra in the Marginal Ice Zone (MIZ). The MIZ is constructed as an array of tens of thousands of compliant circular Ice floes, with randomly selected positions and radii determined by an empirical floe size distribution. Linear potential flow and thin elastic plate theories model the coupled water–Ice system. A new method is proposed to solve the time-harmonic multiple scattering problem under a multidirectional incident wave forcing with random phases. It provides a natural framework for tracking the evolution of the directional properties of a wave field through the MIZ. The attenuation and directional spreading are extracted from ensembles of the wave field with respect to realizations of the MIZ and incident forcing randomly generated from prescribed distributions. The averaging procedure is shown to converge rapidly so that only a small number of simulations need to be performed. Far-field approximations are investigated, allowing efficiency improvements with negligible loss of accuracy. A case study is conducted for a particular MIZ configuration. The observed exponential attenuation of wave energy through the MIZ is reproduced by the model, while the directional spread is found to grow linearly with distance. The directional spreading is shown to weaken when the wavelength becomes larger than the maximum floe size.

  • in situ measurements and analysis of ocean waves in the antarctic Marginal Ice Zone
    Geophysical Research Letters, 2014
    Co-Authors: Michael H Meylan, Luke G Bennetts, Alison L Kohout
    Abstract:

    In situ measurements of ocean surface wave spectra evolution in the Antarctic Marginal Ice Zone are described. Analysis of the measurements shows significant wave heights and peak periods do not vary appreciably in approximately the first 80km of the Ice-covered ocean. Beyond this region, significant wave heights attenuate and peak periods increase. It is shown that attenuation rates are insensitive to amplitudes for long-period waves but increase with increasing amplitude above some critical amplitude for short-period waves. Attenuation rates of the spectral components of the wavefield are calculated. It is shown that attenuation rates decrease with increasing wave period. Further, for long-period waves the decrease is shown to be proportional to the inverse of the period squared. This relationship can be used to efficiently implement wave attenuation through the Marginal Ice Zone in ocean-scale wave models.

  • wave Ice interactions in the Marginal Ice Zone part 1 theoretical foundations
    Ocean Modelling, 2013
    Co-Authors: Timothy D Williams, Dany Dumont, Laurent Bertino, Luke G Bennetts, Vernon A Squire
    Abstract:

    Abstract A wave-Ice interaction model for the Marginal Ice Zone (MIZ) is reported that calculates the attenuation of ocean surface waves by sea Ice and the concomitant breaking of the Ice into smaller floes by the waves. Physical issues are highlighted that must be considered when Ice breakage and wave attenuation are embedded in a numerical wave model or an Ice/ocean model. The theoretical foundations of the model are introduced in this paper, forming the first of a two-part series. The wave spectrum is transported through the Ice-covered ocean according to the wave energy balance equation, which includes a term to parameterize the wave dissipation that arises from the presence of the Ice cover. The rate of attenuation is calculated using a thin-elastic-plate scattering model and a probabilistic approach is used to derive a breaking criterion in terms of the significant strain. This determines if the local wave field is sufficient to break the Ice cover. An estimate of the maximum allowable floe size when Ice breakage occurs is used as a parameter in a floe size distribution model, and the MIZ is defined in the model as the area of broken Ice cover. Key uncertainties in the model are discussed.

Laurent Bertino - One of the best experts on this subject based on the ideXlab platform.

  • wave Ice interactions in the Marginal Ice Zone part 2 numerical implementation and sensitivity studies along 1d transects of the ocean surface
    Ocean Modelling, 2013
    Co-Authors: Timothy D Williams, Dany Dumont, Luke G Bennetts, Vernon A Squire, Laurent Bertino
    Abstract:

    The theoretical foundation of a wave–Ice interaction model is reported in Part 1 of this study. The model incorporates attenuation of ocean surface waves by sea Ice floes and the concomitant breaking of the floes by waves that determines the structure of the Marginal Ice Zone (MIZ). A numerical implementation of the method is presented here. Convergence of the numerical method is demonstrated, as temporal and spatial grids are refined. A semi-analytical method, which does not require time-stepping, is also developed to validate the numerical results, when dispersion is neglected. The wave energy lost during Ice breakage is parameterized, as part of the numerical method. Sensitivity studies are conducted in relation to the energy loss and also dispersive effects, the choIce of the attenuation model, the properties of the wave field, and sea Ice properties such as concentration, thickness and breaking strain. Example simulations intended to represent conditions in the Fram Strait in 2007, which exploit reanalyzed wave and Ice model data, are shown to conclude the results section. These are compared to estimates of MIZ widths based on a concentration criteria, and obtained from remotely-sensed passive microwave images.

  • wave Ice interactions in the Marginal Ice Zone part 1 theoretical foundations
    Ocean Modelling, 2013
    Co-Authors: Timothy D Williams, Dany Dumont, Laurent Bertino, Luke G Bennetts, Vernon A Squire
    Abstract:

    Abstract A wave-Ice interaction model for the Marginal Ice Zone (MIZ) is reported that calculates the attenuation of ocean surface waves by sea Ice and the concomitant breaking of the Ice into smaller floes by the waves. Physical issues are highlighted that must be considered when Ice breakage and wave attenuation are embedded in a numerical wave model or an Ice/ocean model. The theoretical foundations of the model are introduced in this paper, forming the first of a two-part series. The wave spectrum is transported through the Ice-covered ocean according to the wave energy balance equation, which includes a term to parameterize the wave dissipation that arises from the presence of the Ice cover. The rate of attenuation is calculated using a thin-elastic-plate scattering model and a probabilistic approach is used to derive a breaking criterion in terms of the significant strain. This determines if the local wave field is sufficient to break the Ice cover. An estimate of the maximum allowable floe size when Ice breakage occurs is used as a parameter in a floe size distribution model, and the MIZ is defined in the model as the area of broken Ice cover. Key uncertainties in the model are discussed.

  • a wave based model for the Marginal Ice Zone including a floe breaking parameterization
    Journal of Geophysical Research, 2011
    Co-Authors: Dany Dumont, Alison L Kohout, Laurent Bertino
    Abstract:

    [1] The Marginal Ice Zone (MIZ) is the boundary between the open ocean and Ice-covered seas, where sea Ice is significantly affected by the onslaught of ocean waves. Waves are responsible for the breakup of Ice floes and determine the extent of the MIZ and floe size distribution. When the Ice cover is highly fragmented, its behavior is qualitatively different from that of pack Ice with large floes. Therefore, it is important to incorporate wave-Ice interactions into sea Ice–ocean models. In order to achieve this goal, two effects are considered: the role of sea Ice as a dampener of wave energy and the wave-induced breakup of Ice floes. These two processes act in concert to modify the incident wave spectrum and determine the main properties of the MIZ. A simple but novel parameterization for floe breaking is derived by considering alternatively Ice as a flexible and rigid material and by using current estimates of Ice critical flexural strain and strength. This parameterization is combined with a wave scattering model in a one-dimensional numerical framework to evaluate the floe size distribution and the extent of the MIZ. The model predicts a sharp transition between fragmented sea Ice and the central pack, thus providing a natural definition for the MIZ. Reasonable values are found for the extent of the MIZ given realistic initial and boundary conditions. The numerical setting is commensurate with typical Ice-ocean models, with the future implementation into two-dimensional sea Ice models in mind.

Alexander D Fraser - One of the best experts on this subject based on the ideXlab platform.

  • formation processes of sea Ice floe size distribution in the interior pack and its relationship to the Marginal Ice Zone off east antarctica
    Deep-sea Research Part Ii-topical Studies in Oceanography, 2016
    Co-Authors: Takenobu Toyota, Alison Kohout, Alexander D Fraser
    Abstract:

    Abstract To understand the behavior of the Seasonal Ice Zone (SIZ), which is composed of sea-Ice floes of various sizes, knowledge of the floe size distribution (FSD) is important. In particular, FSD in the Marginal Ice Zone (MIZ), controlled by wave–Ice interaction, plays an important role in determining the retreating rates of sea-Ice extent on a global scale because the cumulative perimeter of floes enhances melting. To improve the understanding of wave–Ice interaction and subsequent effects on FSD in the MIZ, FSD measurements were conducted off East Antarctica during the second Sea Ice Physics and Ecosystems eXperiment (SIPEX-2) in late winter 2012. Since logistical reasons limited helicopter operations to two interior Ice regions, FSD in the interior Ice region was determined using a combination of heli-photos and MODIS satellite visible images. The possible effect of wave–Ice interaction in the MIZ was examined by comparison with past results obtained in the same MIZ, with our analysis showing: (1) FSD in the interior Ice region is basically scale invariant for both small- ( 1 km) scale regimes; (2) although fractal dimensions are quite different between these two regimes, they are both rather close to that in the MIZ; and (3) for floes

Dany Dumont - One of the best experts on this subject based on the ideXlab platform.

  • wave Ice interactions in the Marginal Ice Zone part 2 numerical implementation and sensitivity studies along 1d transects of the ocean surface
    Ocean Modelling, 2013
    Co-Authors: Timothy D Williams, Dany Dumont, Luke G Bennetts, Vernon A Squire, Laurent Bertino
    Abstract:

    The theoretical foundation of a wave–Ice interaction model is reported in Part 1 of this study. The model incorporates attenuation of ocean surface waves by sea Ice floes and the concomitant breaking of the floes by waves that determines the structure of the Marginal Ice Zone (MIZ). A numerical implementation of the method is presented here. Convergence of the numerical method is demonstrated, as temporal and spatial grids are refined. A semi-analytical method, which does not require time-stepping, is also developed to validate the numerical results, when dispersion is neglected. The wave energy lost during Ice breakage is parameterized, as part of the numerical method. Sensitivity studies are conducted in relation to the energy loss and also dispersive effects, the choIce of the attenuation model, the properties of the wave field, and sea Ice properties such as concentration, thickness and breaking strain. Example simulations intended to represent conditions in the Fram Strait in 2007, which exploit reanalyzed wave and Ice model data, are shown to conclude the results section. These are compared to estimates of MIZ widths based on a concentration criteria, and obtained from remotely-sensed passive microwave images.

  • wave Ice interactions in the Marginal Ice Zone part 1 theoretical foundations
    Ocean Modelling, 2013
    Co-Authors: Timothy D Williams, Dany Dumont, Laurent Bertino, Luke G Bennetts, Vernon A Squire
    Abstract:

    Abstract A wave-Ice interaction model for the Marginal Ice Zone (MIZ) is reported that calculates the attenuation of ocean surface waves by sea Ice and the concomitant breaking of the Ice into smaller floes by the waves. Physical issues are highlighted that must be considered when Ice breakage and wave attenuation are embedded in a numerical wave model or an Ice/ocean model. The theoretical foundations of the model are introduced in this paper, forming the first of a two-part series. The wave spectrum is transported through the Ice-covered ocean according to the wave energy balance equation, which includes a term to parameterize the wave dissipation that arises from the presence of the Ice cover. The rate of attenuation is calculated using a thin-elastic-plate scattering model and a probabilistic approach is used to derive a breaking criterion in terms of the significant strain. This determines if the local wave field is sufficient to break the Ice cover. An estimate of the maximum allowable floe size when Ice breakage occurs is used as a parameter in a floe size distribution model, and the MIZ is defined in the model as the area of broken Ice cover. Key uncertainties in the model are discussed.

  • a wave based model for the Marginal Ice Zone including a floe breaking parameterization
    Journal of Geophysical Research, 2011
    Co-Authors: Dany Dumont, Alison L Kohout, Laurent Bertino
    Abstract:

    [1] The Marginal Ice Zone (MIZ) is the boundary between the open ocean and Ice-covered seas, where sea Ice is significantly affected by the onslaught of ocean waves. Waves are responsible for the breakup of Ice floes and determine the extent of the MIZ and floe size distribution. When the Ice cover is highly fragmented, its behavior is qualitatively different from that of pack Ice with large floes. Therefore, it is important to incorporate wave-Ice interactions into sea Ice–ocean models. In order to achieve this goal, two effects are considered: the role of sea Ice as a dampener of wave energy and the wave-induced breakup of Ice floes. These two processes act in concert to modify the incident wave spectrum and determine the main properties of the MIZ. A simple but novel parameterization for floe breaking is derived by considering alternatively Ice as a flexible and rigid material and by using current estimates of Ice critical flexural strain and strength. This parameterization is combined with a wave scattering model in a one-dimensional numerical framework to evaluate the floe size distribution and the extent of the MIZ. The model predicts a sharp transition between fragmented sea Ice and the central pack, thus providing a natural definition for the MIZ. Reasonable values are found for the extent of the MIZ given realistic initial and boundary conditions. The numerical setting is commensurate with typical Ice-ocean models, with the future implementation into two-dimensional sea Ice models in mind.