Bibcode
Schüssler, M.; Ferriz-Mas, A.
Bibliographical reference
Geophysical and Astrophysical Fluid Dynamics, vol. 81, Issue 3, pp.233-265
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2
1995
Citations
68
Refereed citations
56
Description
Motivated by the problems of magnetic flux storage and dynamo action in
stars with convection zones, we study the equilibrium and stability of
magnetic flux tubes under the influence of differential rotation and
stratification. The formalism developed in the first paper in this
series is applied to axisymmetric, toroidal flux tubes (flux rings)
lying in planes parallel to the equator at an arbitrary latitude. We
assume mechanical force equilibrium, which requires neutral buoyancy of
the flux tube and a longitudinal internal flow in the direction of
stellar rotation. Stability against isentropic perturbations is
investigated by considering both axisymmetric and non-axisymmetric,
three-dimensional displacements of the equilibrium configuration. For
axisymmetric modes, we find qualitative differences between the
stability criteria for flux tubes within and outside the equatorial
plane, where instability is generally easier to excite and overstable
modes appear. In the case of non-axisymmetric perturbations, the results
of a numerical study with parameter values corresponding to the bottom
of the solar convection zone are discussed. The stability properties
depend in a complicated way on the various parameters (e.g., latitude,
magnetic field, superadiabaticity of the stratification, angular
velocity and its gradient). While the magnetic field value for the onset
of undulatory (Parker) instability with large growth rates is mainly
determined by the stratification and the rotation rate, instabilities at
somewhat lower field strengths with relatively small growth rates depend
strongly on the sign and the value of the angular velocity gradient.