North Atlantic Finite Element Ocean Modeling

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 the 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 net heat 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 is then analyzed and shows many improvements albeit the drift in tracer properties around the 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 10th 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 causes.;To further improve the model 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 was 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.