Tide modelling in the northwest Atlantic

Paturi, Shastri (2007) Tide modelling in the northwest Atlantic. Masters thesis, Memorial University of Newfoundland.

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Abstract

A three dimensional tidal model for the northwest Atlantic was developed including the 8 leading semi-diurnal (M₂, S₂, N₂ and K₂) and diurnal (K₁, O₁, P₁, & Q₁) constituents. Altimetric tides from TOPEX/Poseidon, TOPEX Tandem Mission, JASON-1, ENVISAT, and GFO missions were assimilated into the model. The model was a primitive equation, sigma coordinate system in the vertical, finite difference Princeton Ocean Model (POM). The model used a horizontal rectilinear grid of 1/12° X /12° resolution. The vertical eddy viscosity is computed using the Mellor and Yamada (1982) level 2.5 turbulence model. The model domain covers the region from 75°W to 42°W and 36°N to 66°N. The model is forced at the boundaries with elevations and depth averaged currents for the 8 semidiurnal and diurnal constituents extracted from a North Atlantic Model (Egbert and Erofeeva, 2002). We carried out experiments with homogeneous and stratified (summer-diagnostic) fluid, with and without assimilation, and their results are compared. -- The model reproduced the M₂, S₂, N₂, K₁ and O₁ tidal elevations to an accuracy of 2.1 cm, 1.6 cm, 0.9 cm 1.2 cm & 0.9 cm respectively excluding the Bay of Fundy and Gulf of Maine region. Including the Bay of Fundy and Gulf of Maine region, the accuracy is 10.7 cm, 2.8 cm, 2.5 cm, 1.3 cm and 1.1 cm respectively. Assimilation improved the model tidal elevation by a factor of 40-60%. The semi-diurnal tidal currents agreed to better than the diurnal constituents with observations. The agreement was best for the Georges Bank region indicating the model's capability to handle strong tidal current variability well. Assimilation improved the model tidal currents by roughly 20-30%. An enhancement of the K₁ and O₁ tidal elevation and currents at the shelf edge of Labrador is found in the model, in agreement with theory and observations. -- Inclusion of horizontally and vertically varying stratification indicates that stratification has a significant influence on the vertical profile of currents in the shallow areas. Tidal currents decrease in the bottom boundary, increase significantly in the rest of the bottom layer, and decrease in the upper and middle water column. Stratification improves the K₁ and O₁ currents very slightly by ~5%. Bottom friction and vertical eddy viscosity both played an important role in the shallow areas, especially in the Bay of Fundy, Gulf of Maine, Georges Bank and Scotian Shelf.

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