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TwitterA&A 465, 633-639 (2007)
DOI: 10.1051/0004-6361:20066357
On a long-term dynamics of the magnetised solar tachocline
Eun-jin Kim and N. LeprovostDepartment of Applied Mathematics, University of Sheffield, Sheffield S3 7RH, UK
e-mail: e.kim@sheffield.ac.uk
(Received 7 September 2006 / Accepted 12 January 2007)
Abstract
Aims.We investigate the confinement and long-term dynamics of the
magnetised solar tachocline.
Methods.Starting from first principles, we derive
the values of turbulent transport coefficients
in the magnetised solar tachocline
and then explore the implications
for the confinement and long-term dynamics of the tachocline.
Results.For reasonable parameter values, the turbulent eddy viscosity is
found to be negative, with turbulence enhancing the radial shear
in the tachocline. Both magnetic diffusivity and thermal diffusivity are
severely quenched, with values much smaller than the magnitude of
the eddy viscosity. The effect of the meridional circulation on
momentum transport via the hyperviscosity becomes important when
the radial shear becomes large (larger than the presently inferred
value) due to negative viscosity. The results imply that the
tachocline develops too strong radial shear to be a stationary
Hartmann layer. In the limit of strong radiative damping
where the turbulence is active on very small scales (<10
),
the eddy viscosity can become positive although
its effect is likely to be dominated by the hyperviscosity.
In comparison with the momentum transport, the transport of
magnetic field, heat, and passive particles is more
severely quenched. The results imply that the thickness of the tachocline
is of order
, independent of the strength
of magnetic fields. In addition, the momentum transport is much more
efficient than the particle mixing in the tachocline, consistent
with the observations.
Key words: turbulence -- magnetohydrodynamics (MHD) -- Sun: interior -- Sun: magnetic fields -- Sun: rotation -- waves
© ESO 2007