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Ocean Science An interactive open-access journal of the European Geosciences Union
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Volume 7, issue 4
Ocean Sci., 7, 487–502, 2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ocean Sci., 7, 487–502, 2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 03 Aug 2011

Research article | 03 Aug 2011

Tidal generation of large sub-mesoscale eddy dipoles

W. Callendar1, J. M. Klymak2, and M. G. G. Foreman1 W. Callendar et al.
  • 1Institute of Ocean Sciences, Fisheries and Oceans Canada, Sidney B.C., Canada
  • 2School of Earth and Ocean Sciences, and Dept. of Physics and Astronomy, University of Victoria, B.C., Canada

Abstract. Numerical simulations of tidal flow past Cape St. James on the south tip of Haida Gwaii (Queen Charlotte Islands) are presented that indicate mesoscale dipoles are formed from coalescing tidal eddies. Observations in this region demonstrate robust eddy generation at the Cape, with the primary process being flow separation of buoyant or wind driven outflows forming large anti-cyclonic, negative potential vorticity, Haida Eddies. However, there are other times where dipoles are observed in satellites, indicating a source of positive potential vorticity must also be present. The simulations here build on previous work that implicates oscillating tidal flow past the cape in creating the positive vorticity. Small headland eddies of alternating vorticity are created each tide. During certain tidal cycles, the headland eddies coalesce and self organize in such a way as to create large >20-km diameter eddies that then self-advect into deep water. The self advection speed is faster than the beta drift of anti-cyclones, and the propagation direction appears to be more southerly than typical Haida Eddies, though the model contains no mean wind-driven flows. These eddies are smaller than Haida Eddies, but given their tidal origin, may represent a more consistent source of coastal water that is injected into the interior of the subpolar gyre.

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