| The first part of the thesis investigates the effect of the Gent-McWilliams (GM) parameterization with a variable eddy transfer coefficient in an eddy-permitting ocean model of the subpolar North Atlantic. One of the improvements obtained is a better representation of the overflow waters originating from the Nordic Seas, leading to a more realistic Deep Western Boundary Current, as well as to an increased eddy activity in the deep ocean in the eastern North Atlantic. In addition, the GM velocities "help" the Labrador Sea Water spread from the deep convection region to the currents that surround it, without incurring significant spurious diapycnal mixing. Furthermore, the simulated Labrador Current and the near-surface circulation in the eastern North Atlantic are in a better agreement with flow patterns inferred from observations. Although the variability of the flow is reduced in the experiments with variable eddy transfer coefficients, overall, their use has led to better representations of the general circulation and hydrography in the subpolar North Atlantic. An extended integration of the same model is then examined, focusing on the adjustment of the intermediate and deep waters as well as on model stability. It is shown that the model is able to retain a good representation of the water masses, especially in the Labrador Sea, through the full integration. It is also shown that open boundary conditions do not generate significant model drift, even for integrations approaching a century in length.; In the second part, a new particle model (SPICE) for sea ice dynamics that has no underlying grid is developed and tested. The evolution equations of the pack ice thickness, ice fraction and horizontal area of an arbitrary particle ensure that the ice volume of that particle is conserved. Additionally, each particle preserves its thickness as long as ridging does not occur. A corrected Smoothed Particle Hydrodynamics technique and a variable smoothing length are used for the computation of the spatial derivatives. The model was tested with two different rheologies in an idealized case of an ice pack with a free edge driven by a vortex wind. The simulations with SPICE using a nonlinear viscous rheology are compared with simulations with a more complex Lagrangian finite element model. The predicted locations of the free ice edge compare very well. Because the thickness transport is not plagued by numerical diffusion, the simulated ice edges are not eroded by thickness diffusion. The development of linear kinematic features as narrow bands of intense shearing that separate regions with quasi-uniform motion is simulated in experiments with a viscous-plastic rheology, showing that SPICE is able to simulate complex sea ice dynamics. |
