Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Coronal Alfven speeds in an isothermal atmosphere I. Global properties   Estimating Alfven speeds is of interest in modelling the solar corona,
studying the coronal heating problem and understanding the initiation and
propagation of coronal mass ejections (CMEs). We assume here that the corona is
in a magnetohydrostatic equilibrium and that, because of the low plasma beta,
one may decouple the magnetic forces from pressure and gravity. The magnetic
field is then described by a force-free field for which we perform a
statistical study of the magnetic field strength with height for four different
active regions. The plasma along each field line is assumed to be in a
hydrostatic equilibrium. As a first approximation, the coronal plasma is
assumed to be isothermal with a constant or varying gravity with height. We
study a bipolar magnetic field with a ring distribution of currents, and apply
this method to four active regions associated with different eruptive events.
By studying the global properties of the magnetic field strength above active
regions, we conclude that (i) most of the magnetic flux is localized within 50
Mm of the photosphere, (ii) most of the energy is stored in the corona below
150 Mm, (iii) most of the magnetic field strength decays with height for a
nonlinear force-free field slower than for a potential field. The Alfven speed
values in an isothermal atmosphere can vary by two orders of magnitude (up to
100000 km/s). The global properties of the Alfven speed are sensitive to the
nature of the magnetic configuration. For an active region with highly twisted
flux tubes, the Alfven speed is significantly increased at the typical height
of the twisted flux bundles; in flaring regions, the average Alfven speeds are
above 5000 km/s and depart strongly from potential field values.

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The categories of this paper are: comp-gas
13
The categories of this paper are: quant-ph
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The categories of this paper are: math-ph
22
The categories of this paper are: chao-dyn
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The categories of this paper are: adap-org
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The categories of this paper are: nlin
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The categories of this paper are: patt-sol
5
The categories of this paper are: gr-qc
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The categories of this paper are: q-alg
3
The categories of this paper are: physics
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The categories of this paper are: hep-lat
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The categories of this paper are: plasm-ph
0
The categories of this paper are: hep-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: funct-an
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The categories of this paper are: mtrl-th