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SUMMARY:Influence of external shear and strain on baroclinic vortex alignm
 ent - Carton\, X (Bretagne Occidentale)
DTSTART:20081211T120000Z
DTEND:20081211T123000Z
UID:TALK15616@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:The influence of an external strain (or shear) field on the ev
 olution of two identical vortices at different depths is investigated in a
  two-layer quasi-geostrophic model. The external deformation can include a
  time-varying component. Using point vortex modeling\, symmetric equilibri
 um positions for the vortex doublet are identified and their stability is 
 computed. A time- varying external field can induce resonances on both har
 monic and subharmonic frequencies. A slow time amplitude equation is then 
 computed for the vortex trajectories around their equilibrium positions \;
  its solutions are compared successfully to numerical simulations of a bar
 oclinic point vortex model. The evolution from regular to chaotic trajecto
 ries when the external field amplitude grows\, is analyzed. Finite-area vo
 rtices exhibit the classical regimes of alignment or of co-rotation when s
 ubmitted to external strain and rotation\, but they can also remain statio
 nary at the location of the neutral points for the equivalent point vortic
 es\, or oscillate around these positions. Another regime is evidenced\, in
  which originally very distant vortices are advected towards the center of
  the plane by the large-scale flow\, and finally merge. Thus\, in a dense 
 field of coherent structures\, neighboring vortices can favor the vertical
  alignment of two central vortices\, despite the erosion that they induce 
 on these vortices.
LOCATION:Seminar Room 1\, Newton Institute
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