Graduate Thesis Or Dissertation
 

A model of Arctic Ocean internal waves generated by under-ice topography

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  • The energy levels of internal waves observed during the Arctic Internal Wave Experiment (AIWEX), conducted from the drifting pack ice in the Beaufort Sea, increased as the speed of the ice drift increased. The possibility of these waves being generated by moving pack ice with a corrugated under-side is explored in this paper. An analytical model of internal waves generated by impulsively moving the ice is used to obtain a frequency spectrum of vertical velocity from two reference frames: one fixed relative to the earth and the other moving with the ice. The velocity signal observed from the ice frame simulates the observations from AIWEX instruments moored to the ice. The ocean is assumed to have a constant buoyancy frequency and a finite depth. The ice is approximated as a sum of discrete sinusoidal plane wave components with infinite horizontal extent. These components are determined from a two-dimensional horizontally isotropic wavenumber spectrum, which was obtained from a one-dimensional spectrum of the Beaufort Sea pack ice using the inverse Abet transform. The vertical velocity response of the water particles to the movement of the ice is found as a function of time since initial ice acceleration. The spectrum of the velocity signal, observed over a finite time and averaged over the ocean volume, is compared to velocity spectra from AIWEX observations. Surprisingly the observed spectral shape resembles the modelled spectrum from the fixed frame rather than the ice frame. The discrepancy in the spectral shapes may be due to the non-constant Doppler-shift of the AIWEX observations caused by the changing speed of the ice drift. The model also predicts a more energetic response than was observed; the discrepancy in energy levels may be explained by including a mixed layer in the model.
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