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North Atlantic Finite Element Ocean Modeling Open Access


Other title
Finite element ocean model
Fresh water
Deep Convection
Labrador Sea
Type of item
Degree grantor
University of Alberta
Author or creator
Veluthedathekuzhiyil, Praveen
Supervisor and department
Paul G. Myers (Department of Earth and Atmospheric Sciences)
Examining committee member and department
Francis Poulin (Department of Applied Mathematics, University of Waterloo, ON)
Andrew BG Bush (Department of Earth and Atmospheric Sciences)
John D. Wilson (Department of Earth and Atmospheric Sciences)
Department of Earth and Atmospheric Sciences

Date accepted
Graduation date
Doctor of Philosophy
Degree level
This thesis presents a modified version of the Finite Element Ocean Model (FEOM) developed at Alfred Wegener Institute for Polar and Marine Research (AWI) for the North Atlantic Ocean. A reasonable North Atlantic Ocean simulation is obtained against observational data sets in a Control simulation (CS) where the surface boundary conditions are relaxed to a climatology. The vertical mixing in the model was tuned to represent convection in the model, also the horizontal mixing and diffusion coefficients to represent the changes in the resolution of the model's unstructured grid. In addition, the open boundaries in the model are treated with a sponge layer where tracers are relaxed to climatology. The model is then further modified to accept the atmospheric flux forcing at the surface boundary with an added Northeast flux correction and freshwater forcing from major rivers that are flowing into the North Atlantic Ocean. The impact of this boundary condition on the simulation results are then analyzed and shows many improvements albeit the drift in tracer properties around Gulf Stream region remains as that of the CS case. However a comparison of the vertical sections at Cape Desolation and Cape Farewell with the available observational data sets shows many improvements in this simulation compared to that of the CS case. But the freshwater content in the Labrador Sea interior shows a continued drift as that of the CS case with an improvement towards the $10^{th}$ model year. A detailed analysis of the boundary currents around the Labrador Sea shows the weak offshore transport of freshwater from the West Greenland Current (WGC) as one of the cause. To improve the model further and reasonably represent the boundary currents and associated sub-grid scale eddies in the model, a modified sub-grid scale parameterization based on Gent and McWilliams, 1990 is adopted. The sensitivity of using various approaches in the thickness diffusion parameter ($K_{gm}$) for this parameterization scheme is studied. This includes the use of a constant as well as a spatially varying $K_{gm}$ and both spatially and temporally varying $K_{gm}$ that mimics the baroclinicity of the region of interest. The final approach were able to produce a reasonable North Atlantic Ocean simulation with less drift in the freshwater content of the Labrador Sea interior compared to all the previous simulations. The results are also compared with the observational data sets. Even though few previous studies using an idealized Labrador Sea (Spall, 2004 and Katsman et al., 2004) were able to show the role of seasonal eddy transport of tracer properties into the Labrador Sea interior in setting the convection depth in the region, realistic basin scale modelling of this was still lacking. However the detailed analysis of the boundary currents in this model of the subpolar gyre were able to show the role of the boundary currents and associated eddies in transporting tracer properties across into the Labrador Sea interior and their seasonal variability in setting the convection, preconditioning and restratification phases of the Labrador Sea interior.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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