MAGNETIC MODEL FOR THE SOLAR TACHOCLINE

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MAGNETIC MODEL FOR THE SOLAR TACHOCLINE
L. L. Kitchatinov and G. Ruediger, AIP
Tachocline what is it?
Magnetic field of the solar radiative core
Meridional flow penetration into the core
Long-living modes of poloidal field
Simulated tachocline
Is it stable?
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Internal solar rotation from helioseismology
Gilman Howe (2003)
Graph courtesy NSFs Solar observatory
Tachocline parameters
Thickness
Central radius
Shape prolate
Kosovichev 1996 Wilson et al. 1996 Antia et al.
1998 Charbonneau et al. 1999
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There should be an efficient link between low
and high latitudes near the top of radiative
core. There should be an efficient radial link
deeper down. The radial link cannot be done by
mixing (Lithium abundance). Both links can be
provided by an internal poloidal magnetic field.
The internal field should be almost horizontal
near the top of the core.
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Meridional flow penetration beneath the
convection zone
Gilman Miesch (2003), Kitchatinov Ruediger
(2005)
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Penetration parameters
Characteristic depth
for microscopic viscosity
for eddy viscosity below
Characteristic times
- shearing time
- diffusion time
- advection time
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Axial symmetry
The poloidal field equation,
integrated across the penetration layer gives the
new boundary condition
Eigenmode equation
After Stix Skaley (1990)
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Poloidal field eigenmodes
Openness parameter
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Tachocline equations
Top boundary conditions
The amplitude, , of poloidal field remains
the model parameter.
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Rm - dependence
Rotation
Poloidal field
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Field strength dependence (Rm 1000)
Analytical estimations
Tachocline thickness
Toroidal field strength
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Eigenmodes of poloidal field
Rotation
The polar cusp is a consequence of axial symmetry
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Stability
Stability map for the model by Gilman Fox
(1997)
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Conclusions
The slender solar tachocline can result from a
week (0.001 G) internal poloidal field if the
field is almost totally locked to the radiative
core
The internal field geometry required for the
tachocline formation can be ensured by a shallow
penetration of meridional flow beneath the base
of convection zone
The tachocline is stable