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Regular and Chaotic Dynamics

, Volume 15, Issue 1, pp 66–83 | Cite as

Homostrophic vortex interaction under external strain, in a coupled QG-SQG model

  • X. Perrot
  • J. N. Reinaud
  • X. Carton
  • D. G. Dritschel
Research Articles

Abstract

The interaction between two co-rotating vortices, embedded in a steady external strain field, is studied in a coupled Quasi-Geostrophic — Surface Quasi-Geostrophic (hereafter referred to as QG-SQG) model. One vortex is an anomaly of surface density, and the other is an anomaly of internal potential vorticity. The equilibria of singular point vortices and their stability are presented first. The number and form of the equilibria are determined as a function of two parameters: the external strain rate and the vertical separation between the vortices. A curve is determined analytically which separates the domain of existence of one saddle-point, and that of one neutral point and two saddle-points. Then, a Contour-Advective Semi-Lagrangian (hereafter referred to as CASL) numerical model of the coupled QG-SQG equations is used to simulate the time-evolution of a sphere of uniform potential vorticity, with radius R at depth −2H interacting with a disk of uniform density anomaly, with radius R, at the surface. In the absence of external strain, distant vortices co-rotate, while closer vortices align vertically, either completely or partially (depending on their initial distance). With strain, a fourth regime appears in which vortices are strongly elongated and drift away from their common center, irreversibly. An analysis of the vertical tilt and of the horizontal deformation of the internal vortex in the regimes of partial or complete alignment is used to quantify the three-dimensional deformation of the internal vortex in time. A similar analysis is performed to understand the deformation of the surface vortex.

Key words

coupled QG-SQG model point-vortex CASL 

MSC2000 numbers

86A05 76U05 76B70 76B47 76M25 

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Copyright information

© Pleiades Publishing, Ltd. 2010

Authors and Affiliations

  • X. Perrot
    • 1
  • J. N. Reinaud
    • 2
  • X. Carton
    • 1
  • D. G. Dritschel
    • 2
  1. 1.Laboratoire de Physique des OcéansUBO, UEBBrestFrance
  2. 2.Mathematical Institute North HaughUniversity of St AndrewsSt AndrewsScotland, UK

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