The effect of ageostrophy on the stability of thin oceanic vortices

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Abstract

This paper examines the stability of vortices in a two-layer ocean on the f-plane. The mean depth h̄1 of the upper layer is assumed to be much smaller than the depth h̄2 of the lower layer. Using the primitive equations, we derive an asymptotic criterion for baroclinic instability of compensated (i.e. confined to the upper layer) vortices. Surprisingly, it coincides exactly with a similar criterion derived from the quasigeostrophic equations [Benilov, E.S., 2003. Instability of quasigeostrophic vortices in a two-layer ocean with thin upper layer. J. Fluid Mech. 475, 303-331]. Thus, to leading order in h̄1/h̄2, ageostrophy does not affect the stability properties of thin compensated vortices. As a result, whether a vortex is stable or not, depends on its shape, not amplitude (although the growth rate of an unstable vortex does depend on its amplitude).

Original languageEnglish
Pages (from-to)211-226
Number of pages16
JournalDynamics of Atmospheres and Oceans
Volume39
Issue number3-4
DOIs
Publication statusPublished - May 2005

Keywords

  • Ageostrophy
  • Baroclinic instability
  • Ocean vortices

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