Alternating zonal flows in a two-layer wind-driven ocean |
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| Authors: | Yuusuke Tanaka Kazunori Akitomo |
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| Institution: | (1) College of Marine Science, University of South Florida, St. Petersburg, FL 33701, USA;(2) Department of Mechanical Engineering, Ben-Gurion University of the Negev, Beer-Sheva, 84105, Israel;(3) Perlstone Center for Aeronautical Engineering Studies, Ben-Gurion University of the Negev, Beer-Sheva, 84105, Israel |
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| Abstract: | Alternating zonal flows in an idealized wind-driven double-gyre ocean circulation have been investigated using a two-layer
shallow-water eddy-permitting numerical model. While the alternating zonal flows are found almost everywhere in the time-mean
zonal velocity field, their meridional scales differ from region to region. In the subpolar western boundary region, where
the energetic eddy activity induces quasi two-dimensional turbulence, the alternating zonal flows are generated by the inverse
energy cascade and its arrest by Rossby waves, and the meridional scale of the flows corresponds well to the Rhines scale.
In the eastern part of the basin, where barotropic basin modes are dominant, the zonal structure is formed through the nonlinear
effect of the basin modes and is wider than the Rhines scale. Both effects are likely to form zonal structure between the
two regions. These results show that Rossby basin modes become an important factor in the formation of alternating zonal flows
in a closed basin in addition to the arrest of the inverse energy cascade by Rossby waves. The wind-driven general circulation
associated with eddy activities plays an essential role in determining which mechanism of the alternating zonal flows is possible
in each region. |
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