Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Surface Alfven waves in solar flux tubes   Magnetohydrodynamic (MHD) waves are ubiquitous in the solar atmosphere.
Alfven waves and magneto-sonic waves are particular classes of MHD waves. These
wave modes are clearly different and have pure properties in uniform plasmas of
infinite extent only. Due to plasma non-uniformity MHD waves have mixed
properties and cannot be classified as pure Alfven or magneto-sonic waves.
However, vorticity is a quantity unequivocally related to Alfven waves as
compression is for magneto-sonic waves. Here, we investigate MHD waves
superimposed on a one-dimensional non-uniform straight cylinder with constant
magnetic field. For a piecewise constant density profile we find that the
fundamental radial modes of the non-axisymmetric waves have the same properties
as surface Alfven waves at a true discontinuity in density. Contrary to the
classic Alfveen waves in a uniform plasma of infinite extent, vorticity is zero
everywhere except at the cylinder boundary. If the discontinuity in density is
replaced with a continuous variation of density, vorticity is spread out over
the whole interval with non-uniform density. The fundamental radial modes of
the non-axisymmetric waves do not need compression to exist unlike the radial
overtones. In thin magnetic cylinders the fundamental radial modes of the
non-axisymmetric waves with phase velocities between the internal and the
external Alfven velocities can be considered as surface Alfven waves. On the
contrary, the radial overtones can be related to fast-like magneto-sonic modes.

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The categories of this paper are: hep-ph
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The categories of this paper are: physics
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The categories of this paper are: gr-qc
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The categories of this paper are: q-alg
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The categories of this paper are: acc-phys
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The categories of this paper are: funct-an
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The categories of this paper are: nlin
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The categories of this paper are: math-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: patt-sol
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The categories of this paper are: solv-int
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The categories of this paper are: hep-ex
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The categories of this paper are: eess
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The categories of this paper are: adap-org
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The categories of this paper are: ao-sci
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The categories of this paper are: chao-dyn