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| Paper: |
Vortices in Astrophysical Discs |
| Volume: |
160, Astrophysical Discs: An EC Summer School |
| Page: |
341 |
| Authors: |
Fridman, A. M.; Khoruzhii, O. V. |
| Abstract: |
Dynamical theory of astrophysical discs predicts two different kinds of vortices: ``linear'' and ``nonlinear.'' If galactic spiral arms are density waves, linear vortices in the velocity field are predicted at infinitesimal amplitude, and both spirals and vortices grow together at equal rate. The centres of linear vortices lie in the neighborhood of the corotation circle and between spiral arms for both spiral generation mechanisms considered here. Linear vortices (anticyclones), which were predicted on the basis of experiments with rotating shallow water, have been observed in spiral galaxies both when the rotation curve has a velocity jump and when it is smooth. There are at least two kinds of nonlinear vortices which occur at a finite amplitude only: Rossby vortices and nonlinear convection. Rossby vortices are described by a 2-D equation, derived from the 3-D nonlinear hydrodynamical equations, which has both scalar and vector nonlinearities. Rossby vortices are independent of the presence of spiral waves and consist of two kinds: single solitary vortices (cyclones and anticyclones) and double solitary vortices (modons). Nonlinear convection is described by the time-averaged nonlinear 3-D hydrodynamical equations taking into account the vertical structure of the disc. It is caused by nonlinear Reynolds stresses induced by the spiral density wave and has a form of four, large-scale, toroidal vortices separated by the vertical cylindrical surface at corotation and the central plane of the disc. |
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