Kohout, Alison

Alison Kohout (PHD student)

Research topic: Two dimensional wave scattering in the MIZ

The sea-ice which forms in the polar oceans plays a key role in driving the world's oceanic circulatory system and hence the world's climatic system. It is therefore important to understand the processes which influence the extent of this sea-ice. \citet{squire95,wadhams00} have evidence suggesting that ocean waves play a major role in the fracturing of ice-covered seas. The analysis of this phenomena involves many complicated variables and considerable idealisation is required. One aspect which is critical to understand is the decay of wave energy through the Marginal Ice Zone (MIZ).

The MIZ is an interfacial region which forms at the boundary of open and frozen oceans. It consists of a vast field of ice floes and is subject to considerable wave action due to its proximity to the open ocean. Experiments have shown that the wave intensity decays exponentially with distance from the open ocean and that this rate of decay is highly dependent on the wave period \citep{directional86,attenuation88}.

A number of models for wave propagation in the marginal ice zone have been presented. The most sophisticated were the fully three dimensional models using a coupling of solutions for individual ice floes with a transport equation \citep{Masson_Le,jgrrealism}. These models, which were derived separately, have been recently shown to be almost identical \citep{ocean_modelling06}. Another three-dimensional model was developed by \citet{dixon_squire01} based on the coherent potential approximation. We present here a much simpler model based on a two-dimensional solution. Although much simpler, this model has a number of advantages over the three-dimensional models, the most important being that it is much less computationally demanding. We also believe that a simple model is the best place to begin to make comparisons with data and to test and debug the more sophisticated models.

The two-dimensional solution is based on a matched eigenfunction expansion. The model is described in detail in \citet{elastic_plates06} where the solution is carefully analysed for energy conservation, compared with previous results and compared to a series of experiments which were performed by \citet{sakai_hanai02} using floating plastic sheets in a two-dimensional wave tank. We are therefore confident that the numerical solution presented here is correct.

In this paper, we describe the two dimonsional model and analyse it in repsect to the MIZ. We compare our results against a series of field experiments carried out by the Scott Polar Research Institute (SPRI) to measure wave energy attenuation rates in the marginal ice zones of the Greenland and Bering Seas. These field experiments are the only ones of their kind and are further discussed in \citet{wadhams_squire88}.