A Three-Dimensional Numerical Simulation of Hudson Bay Summer Ocean Circulation: Topographic Gyres, Separations, and Coastal Jets

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  • 1 Department Of Atmospheric and Oceanic Sciences and Centre for Climate and Global Change Research, McGi11 University, Montreal, Quebec, Canada
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Abstract

The summer ocean circulation in Hudson Bay is studied numerically using the Blumberg-Mellor model with a 27.5 km × 27.5 km horizontal grid and a realistic bottom topography. In the control run 1) monthly climatological forcing fields of wind stress, oceanic inflow/outflow, and salt and heat fluxes are used. In addition, results are presented for a number ot sensitivity experiments: 2) no topography (otherwise conditions are identical to the control run), 3) no wind forcing, 4) no oceanic inflow/outflow, 5) no heat and salt fluxes, 6) no temperature and salinity variations, and 7) without the nonlinear terms.

While the overall simulated circulation in Hudson Bay is cyclonic, the strong steering of the flow by the bathymetry is particularly noticeable. Mesoscale topographic gyres are simulated, and the separation of the coastal current due to topographic bumps occurs in several locations. The simulated circulation also has well-developed vorticity features and narrow, density-driven coastal jets along the western, southern, and eastern shores of Hudson Bay, which enhance the wind-driven alongshore current. From various sensitivity experiments, it is estimated that the total transport of 0.55 Sv (Sv ≡ 106 m3 s−1) is made up of a 0.23 Sv wind-driven transport, a 0.12 Sv density-driven transport, and a 0.2 Sv inflow/outflow induced transport. It is also found that the wind-driven circulation in Hudson Bay shows a recirculation, whereas the density-driven and inflow/outflow induced transports do not.

A one-dimensional version of the model is also used to simulate the thermohaline vertical structure over a seasonal cycle. In particular, the observed deepening of the mixed layer in fall is reasonably well reproduced by the model.

Abstract

The summer ocean circulation in Hudson Bay is studied numerically using the Blumberg-Mellor model with a 27.5 km × 27.5 km horizontal grid and a realistic bottom topography. In the control run 1) monthly climatological forcing fields of wind stress, oceanic inflow/outflow, and salt and heat fluxes are used. In addition, results are presented for a number ot sensitivity experiments: 2) no topography (otherwise conditions are identical to the control run), 3) no wind forcing, 4) no oceanic inflow/outflow, 5) no heat and salt fluxes, 6) no temperature and salinity variations, and 7) without the nonlinear terms.

While the overall simulated circulation in Hudson Bay is cyclonic, the strong steering of the flow by the bathymetry is particularly noticeable. Mesoscale topographic gyres are simulated, and the separation of the coastal current due to topographic bumps occurs in several locations. The simulated circulation also has well-developed vorticity features and narrow, density-driven coastal jets along the western, southern, and eastern shores of Hudson Bay, which enhance the wind-driven alongshore current. From various sensitivity experiments, it is estimated that the total transport of 0.55 Sv (Sv ≡ 106 m3 s−1) is made up of a 0.23 Sv wind-driven transport, a 0.12 Sv density-driven transport, and a 0.2 Sv inflow/outflow induced transport. It is also found that the wind-driven circulation in Hudson Bay shows a recirculation, whereas the density-driven and inflow/outflow induced transports do not.

A one-dimensional version of the model is also used to simulate the thermohaline vertical structure over a seasonal cycle. In particular, the observed deepening of the mixed layer in fall is reasonably well reproduced by the model.

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