References

Ocean Science

Ocean Sci.

1812-0792

Copernicus Publications

Göttingen, Germany

10.5194/os-3-179-2007

Tidal modulation of two-layer hydraulic exchange flows

Frankcombe

L. M.

¹ ² Hogg

A. McC.

Research School of Earth Sciences, The Australian National University, Canberra, Australia

now at: Institute for Marine and Atmosphere Research Utrecht, Department of Physics and Astronomy, Utrecht University, The Netherlands

26 04 2007

3 2 179 188

2007

This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 Generic License. To view a copy of this licence, visit https://creativecommons.org/licenses/by-nc-sa/2.5/

This article is available from https://os.copernicus.org/articles/3/179/2007/os-3-179-2007.html

The full text article is available as a PDF file from https://os.copernicus.org/articles/3/179/2007/os-3-179-2007.pdf

Time-dependent, two layer hydraulic exchange flow is studied using an idealised shallow water model. It is found that barotropic time-dependent perturbations, representing tidal forcing, increase the baroclinic exchange flux above the steady hydraulic limit, with flux increasing monotonically with tidal amplitude (measured either by height or flux amplitude over a tidal period). Exchange flux also depends on the non-dimensional tidal period, γ, which was introduced by by Helfrich (1995). When tidal amplitude is characterised by the barotropic flux amplitude, exchange flux is a monotonic function of γ as predicted by Helfrich (1995). However, the relationship between the (imposed) free surface amplitude and flux amplitude is complicated by reflections within the channel and by the baroclinic response of the two layer system, leading to a non-monotonic relationship between the height amplitude and γ.

References 1

Armi, L.: The hydraulics of two flowing layers with different densities, J. Fluid Mech., 163, 27–58, 1986.

Armi, L. and Farmer, D M.: Maximal two-layer exchange through a contraction with barotropic net flow, J. Fluid Mech., 164, 27–51, 1986.

Armi, L. and Farmer, D M.: A Generalization of the concept of Maximal Exchange in a Strait, J. Geophys. Res., 92, 14 679–14 680, 1987.

Bray, N., Ochoa, W J., and Kinder, T.: The role of the interface in exchange through the Strait of Gibraltar, J. Geophys. Res., 100, 10 755–10 776, 1995.

Harvey, J. and Arhan, M.: The Water Masses of the Central North Atlantic in 1983–84, J. Phys. Oceanogr., 18, 1855–1875, 1988.

Helfrich, K L.: Time-dependent two-layer hydraulic exchange flow, J. Phys. Oceanogr., 25, 359–373, 1995.

Ivey, G N.: Stratification and mixing in sea straits, Deep-Sea Res. II, 51, 441–453, 2004.

Nycander, J. and Döös, K.: Open boundary conditions for barotropic waves, J. Geophys. Res., 108(C5), https://doi.org/10.1029/2002JC001 529, 2003.

Phu, A.: Tidally forced exchange flows, Honours thesis, University of Western Australia, 2001.

Stigebrandt, A.: On the effects of barotropic current fluctuations on the two-layer transport capacity of a constriction, J. Phys. Oceanogr., 7, 118–122, 1977.

Sy, A.: Investigation of large-scale circulation patterns in the Central North Atlantic: the North Atlantic Current, the Azores Current, and the Mediterranean Water plume in the area of the Mid-Atlantic Ridge, Deep Sea Res., 35, 383–413, 1988.

Wood, I R.: ~A lock exchange flow, J. Fluid Mech., 42, 671–687, 1970.