Locally-induced nonlinear modes and multiple equilibria in planetary fluids |
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Authors: | T Yamagata K Sakamoto M Arai |
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Institution: | (1) Research Institute for Applied Mechanics, Kyushu University, 816 Kasuga, Japan;(2) Department of Physics, Kyushu University, 812 Fukuoka, Japan |
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Abstract: | It is demonstrated that nonlinear Rossby modes, such as modons and IG eddies, can be excited in planetary fluids by a sufficiently strong forcing of potential vorticity. When a weak forcing is balanced with a weak dissipation, two (linear and nonlinear) equilibrium states can be produced, depending on the initial condition. When the fluid is inviscid, a sufficiently strong steady forcing may generate a sequence of propagating nonlinear eddies. A weak forcing, by contrast, only generates linear Rossby waves. The criterion which divides the high amplitude nonlinear state and the low amplitude linear state may be interpreted in terms of a ratio of a time necessary to force the eddy to a time for a fluid particle to circulate about the nonlinear eddy once. |
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Keywords: | Nonlinear coherent structures modons IG eddies local multiple equilibria long Rossby waves potential vorticity |
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