Ocean wave scattering by natural sea ice transects

Abstract

Ocean waves propagate in continuous sea ice as flexural‐gravity waves, so named because their dispersion is influenced by bending of the ice plate and by buoyancy. Such waves are scattered by topographic heterogeneity in the ice, e.g., features like pressure ridges, yet current models fail to account for the complexity that is symptomatic of sea ice. Here a two‐dimensional wave scattering model is described that allows real data from natural sea ice to be assimilated rather than synthetic ice terrain. On the basis of linear wave theory and the elastic thin plate equation, the model assumes an unbroken compliant sea ice cover with no free edges and uses Green's Functions to obtain an integral equation that is solved numerically. While scattering in physical stretches of sea ice can vary greatly, all transects behave as low‐pass filters and can display resonances that relate to how features are separated or to transect length, the latter being an undesirable trait of the model. In the paper an association is made between the statistical properties of the sea ice terrain and the nature of the scattering that results. Not unexpectedly, sea ice with greater relative draft variation is more reflective. It is proposed that this observation can be used to identify the draft variation for an unknown transect if its scattering response is known. Finally, the progression of median energy density for ensembles of similarly sampled transects is examined at wave periods of less than 10 s and is found to decay exponentially with distance traveled, in accord with the few observations available.