Interaction between a surface quasi-geostrophic buoyancy filament and an internal vortex

Type Article
Date 2016
Language English
Author(s) Reinaud Jean N.1, Dritschel David G.1, Carton Xavier2
Affiliation(s) 1 : Univ St Andrews, Math Inst, St Andrews, Fife, Scotland.
2 : UBO UBL, IUEM, Lab Oceanog Phys & Spatiale, Plouzane, France.
Source Geophysical And Astrophysical Fluid Dynamics (0309-1929) (Taylor & Francis Ltd), 2016 , Vol. 110 , N. 6 , P. 461-490
DOI 10.1080/03091929.2016.1233331
WOS© Times Cited 13
Keyword(s) Vortex dynamics, semi-quasigeostrophy, quasigeostrophy
Abstract

This paper focuses on the nonlinear interaction between a surface quasi-geostrophic buoyancy filament and an internal vortex. We first revisit the stability of an isolated buoyancy filament. The buoyancy profile considered is continuous and leads to a continuous velocity field, albeit one with infinite shear just outside its edge. The stability properties of an isolated filament help to interpret the unsteady interaction with a sub-surface (internal) vortex studied next. We find that, in all cases, the filament breaks into billows, analogous in form to those occurring in Kelvin-Helmholtz shear instability. For intense buoyancy filaments, the vortex itself may undergo strong deformations, including being split into several pieces. Generally, the nonlinear interaction causes both the filament and the vortex to lose their respective self-energies to the energy of interaction. The flow evolution depends sensitively on whether the vertical vorticity of the filament and the vortex have the same or opposite signs - termed cooperative and adverse shear respectively. In cooperative shear, the filament rolls up into a coherent surface eddy above a vortex initially placed below it, whereas in adverse shear, buoyancy is expelled above the vortex. Although sufficiently great shear induced by the buoyancy filament may split the vortex in both cases, adverse shear is significantly more destructive.

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