pure and applied geophysics

, Volume 133, Issue 4, pp 733–748 | Cite as

Locally-induced nonlinear modes and multiple equilibria in planetary fluids

  • T. Yamagata
  • K. Sakamoto
  • M. Arai


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.

Key words

Nonlinear coherent structures modons IG eddies local multiple equilibria long Rossby waves potential vorticity 


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Copyright information

© Birkhäuser Verlag 1990

Authors and Affiliations

  • T. Yamagata
    • 1
  • K. Sakamoto
    • 1
  • M. Arai
    • 2
  1. 1.Research Institute for Applied MechanicsKyushu UniversityKasugaJapan
  2. 2.Department of PhysicsKyushu UniversityFukuokaJapan

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