Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Polar confinement of the Sun's interior magnetic field by laminar
  magnetostrophic flow   The global-scale interior magnetic field needed to account for the Sun's
observed differential rotation can be effective only if confined below the
convection zone in all latitudes, including the polar caps. Axisymmetric
nonlinear MHD solutions are obtained showing that such confinement can be
brought about by a very weak downwelling flow U~10^{-5}cm/s over each pole.
Such downwelling is consistent with the helioseismic evidence. All three
components of the magnetic field decay exponentially with altitude across a
thin "magnetic confinement layer" located at the bottom of the tachocline. With
realistic parameter values, the thickness of the confinement layer ~10^{-3} of
the Sun's radius. Alongside baroclinic effects and stable thermal
stratification, the solutions take into account the stable compositional
stratification of the helium settling layer, if present as in today's Sun, and
the small diffusivity of helium through hydrogen, chi. The small value of chi
relative to magnetic diffusivity produces a double boundary-layer structure in
which a "helium sublayer" of smaller vertical scale is sandwiched between the
top of the helium settling layer and the rest of the confinement layer.
Solutions are obtained using both semi-analytical and purely numerical,
finite-difference techniques. The confinement-layer flows are magnetostrophic
to excellent approximation. More precisely, the principal force balances are
between Lorentz, Coriolis, pressure-gradient and buoyancy forces, with relative
accelerations and viscous forces negligible. This is despite the kinematic
viscosity being somewhat greater than chi. We discuss how the confinement
layers at each pole might fit into a global dynamical picture of the solar
tachocline. That picture, in turn, suggests a new insight into the early Sun
and into the longstanding enigma of solar lithium depletion.

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The categories of this paper are: math
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The categories of this paper are: nlin
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The categories of this paper are: physics
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The categories of this paper are: hep-ex
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The categories of this paper are: mtrl-th
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The categories of this paper are: nucl-th
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The categories of this paper are: atom-ph
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The categories of this paper are: cs
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The categories of this paper are: acc-phys
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The categories of this paper are: gr-qc
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The categories of this paper are: stat
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The categories of this paper are: nucl-ex
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The categories of this paper are: q-bio
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The categories of this paper are: comp-gas
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The categories of this paper are: dg-ga
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The categories of this paper are: adap-org