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Abstract: This paper investigates the attenuation and directional spreading of large amplitude waves traveling through pancake ice. Directional spectral density is analyzed from in situ wave buoy data collected during a 3‐day storm event in October 2015 in the Beaufort Sea. Two proxy metrics for wave amplitude obtained from energy density spectra, namely, spectral amplitude and significant wave height, are used to track the waves as they propagate along transects through the array of buoys in the predominantly pancake ice field. Two types of wave buoys are used in the analysis and compared, exhibiting significant differences in the wave energy density and directionality estimates. Although exponential decay is observed predominantly, one of the two buoy types indicates a potential positive correlation between wave energy density and the occurrence of linear wave decay, as opposed to exponential decay, in accord with recent observations in the Antarctic marginal ice zone. Factors affecting the validity of this observation are discussed. An empirical power law with exponent 2.2 is also found to hold between the exponential attenuation coefficient and wave frequency. The directional content of the wave spectrum appears to decrease consistently along the wave transects, confirming that wave energy is being dissipated by the pancake ice as opposed to being scattered by ice cakes. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A three-dimensional model of ocean-wave scattering in the marginal ice zone is constructed using linear theory under time-harmonic conditions. Individual floes are represented by circular elastic plates and are permitted to have a physically realistic draught. These floes are arranged into a finite number of parallel rows, and each row possesses an infinite number of identical floes that are evenly spaced. The floe properties may differ between rows, and the spacing between the rows is arbitrary. The vertical dependence of the solution is expanded in a finite number of modes, and through the use of a variational principle, a finite set of two-dimensional equations is generated from which the full-linear solution may be retrieved to any desired accuracy. By dictating the periodicity in each row to be identical, the scattering properties of the individual rows are combined using transfer matrices that take account of interactions between both propagating and evanescent waves. Numerical results are presented that investigate the differences between using the three-dimensional model and using a two-dimensional model in which the rows are replaced with strips of ice. Furthermore, Bragg resonance is identified when the rows are identical and equi-spaced, and its reduction when the inhomogeneities, that are accommodated by the model, are introduced is shown. [ABSTRACT FROM AUTHOR]

Arctic sea-ice contains imperfections such as cracks, leads and pressure ridges that scatter flexural-gravity waves. Models for predicting scattering have been described in the literature, concentrating mainly on singular isolated features with simplified shapes or on arrays of such features. In reality ridges are seldom simple and leads are rarely entirely free of ice. Here we describe a model in which the scattering by a sheet of arbitrary thickness can be simulated. Linear wave theory and Green's functions are used to derive the governing equations for a numerical model of a two-dimensional (in the vertical) system. We examine wave scattering by random ice sheets, identifying trends in behavior as the wave period and the length, median thickness and variance of the sheet are changed. It has been suggested that wave scattering could be used to identify sea-ice thickness, a task which is difficult or expensive by other methods, and here we examine a technique by which this could potentially be achieved. However, a large data base is necessary for this to work and this may limit the practicality of the approach. [ABSTRACT FROM AUTHOR]