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Circulation around islands and ridges
I am studying the influences of planetary scale topographic features such as islands and abyssal
ridges on the mean and low frequency variability of the large scale circulation using both numerical models
and simple theories. The circulation integral around an island places a strong constraint on the
properties of the flow, both in the vicinity of the island and in the adjacent basins. Single islands or island
chains allow for the passage of some forms of low frequency variability quite freely, while other forms are
entirely blocked by the topography. Interesting circulation features arise in the mean flow, such as
recirculation gyres, jets, and eastern boundary currents as a result of circulation constraints around the topography.
Although most recent efforts have been directed towards understanding the large-scale wind-forced circulation
around islands, buoyancy-forcing can also alter the exchange between adjacent basins, particularly if it is
concentrated along the western coast of the island or ridge. Diapycnal mixing near a boundary can result
in significant dissipation, which results in a pressure drop along the boundary near the mixing region.
This pressure drop must be balanced elsewhere along the island perimeter, giving rise to the possibility
that diapycnal mixing, due either to air-sea exchange or internal wave breaking, can drive a large-scale
circulations around topographic features that may extend far from the region of mixing.
This work has been generously supported through grants from the
National Science Foundation and the Office of Naval Research.
Recent manuscripts on these subjects :
| Pedlosky, J., R. Iacono, E. Napolitano, M. A. Spall, 2011:
The two-layer skirted island.
J. Mar. Res,69, 347-382.
Pratt, L. J., and M. A. Spall, 2003. A Porous Medium Theory for Geostrophic
Flow Through Ridges and Archipelagos. Journal of Physical
Oceanography , 33,2702-2718.
Spall, M. A., 2003. Islands in Zonal Flow. Journal of Physical
Oceanography , 33, 2689-2701.
Spall, M. A., 2002. Wind- and buoyancy-forced upper ocean circulation in two-strait marginal seas with
application to the Japan / East Sea. Journal of Geophysical Research , 107(C1), 6.1-6.12.
Spall, M. A., 2000. Buoyancy-forced circulation around islands and ridges. Journal of Marine Research,
Pedlosky, J. and M. A. Spall, 1999. Rossby normal modes in basins with barriers. Journal of Physical
Oceanography, 29(9), 2332-2349.
Pedlosky, J., L. J. Pratt, M. A. Spall, K. R. Helfrich, 1997. Circulation around islands and
ridges. Journal of Marine Research, 55(6), 1199-1251.