Simulating the three-dimensional circulation and hydrography of Halifax Harbour using a multi-nested coastal ocean circulation model |
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Authors: | Shiliang Shan Jinyu Sheng Keith Richard Thompson David Alexander Greenberg |
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Institution: | (1) Department of Oceanography, Dalhousie University, Halifax, NS, Canada;(2) Fisheries and Oceans Canada, Bedford Institute of Oceanography, Dartmouth, NS, Canada;; |
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Abstract: | Halifax Harbour is located on the Atlantic coast of Nova Scotia, Canada. It is one of the world’s largest, ice-free natural
harbours and of great economic importance to the region. A good understanding of the physical processes controlling tides,
flooding, transport and dispersion, and hydrographic variability is required for pollution control and sustainable development
of the Harbour. For the first time, a multi-nested, finite difference coastal ocean circulation model is used to reconstruct
the three-dimensional circulation and hydrography of the Harbour and its variability on timescales of hours to months for
2006. The model is driven by tides, wind and sea level pressure, air-sea fluxes of heat, and terrestrial buoyancy fluxes associated
with river and sewage discharge. The predictive skill of the model is assessed by comparing the model simulations with independent
observations of sea level from coastal tide gauges and currents from moored instruments. The simulated hydrography is also
compared against a new monthly climatology created from all available temperature and salinity observations made in the Harbour
over the last century. It is shown that the model can reproduce accurately the main features of the observed tides and storm
surge, seasonal mean circulation and hydrography, and wind driven variations. The model is next used to examine the main physical
processes controlling the circulation and hydrography of the Harbour. It is shown that non-linear interaction between tidal
currents and complex topography occurs over the Narrows. The overall circulation can be characterized as a two-layer estuarine
circulation with seaward flow in the thin upper layer and landward flow in the broad lower layer. An important component of
this estuarine circulation is a relatively strong, vertically sheared jet situated over a narrow sill connecting the inner
Harbour to the deep and relatively quiescent Bedford Basin. Local wind driven variability is strongest in winter as expected
but it is also shown that a significant part of the temperature and salinity variability is driven by physical processes occurring
on the adjacent inner continental shelf, especially during storm and coastal upwelling events. |
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