Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Numerical simulation of excitation and propagation of helioseismic MHD
  waves: Effects of inclined magnetic field   Investigation of propagation, conversion, and scattering of MHD waves in the
Sun is very important for understanding the mechanisms of observed oscillations
and waves in sunspots and active regions. We have developed 3D linear MHD
numerical model to investigate influence of the magnetic field on excitation
and properties of the MHD waves. The results show that the magnetic field can
substantially change the properties of the surface gravity waves (f-mode), but
their influence on the acoustic-type waves (p-modes) is rather moderate.
Comparison our simulations with the time-distance helioseismology results from
SOHO/MDI shows that the travel time variations caused by the inclined magnetic
field do not exceed 25% of the observed amplitude even for strong fields of
1400-1900 G. This can be an indication that other effects (e.g. background
flows and non-uniform distribution of magnetic field) can contribute to the
observed travel time variations. The travel time variations caused by the wave
interaction with magnetic field are in phase with the observations for strong
fields of 1400-1900 G if Doppler velocities are taken at the height of 300 km
above the photosphere where plasma parameter beta<<1. The simulations show that
the travel times only weakly depend on the height of velocity observation. For
the photospheric level the travel times are systematically smaller on
approximately 0.12 min then for the hight of 300 km above the photosphere for
all studied ranges of the magnetic field strength and inclination angles. The
numerical MHD wave modeling and new data from the HMI instrument of the Solar
Dynamics Observatory will substantially advance our knowledge of the wave
interaction with strong magnetic fields on the Sun and improve the local
helioseismology diagnostics.

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The categories of this paper are: physics
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The categories of this paper are: alg-geom
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The categories of this paper are: atom-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: comp-gas
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The categories of this paper are: econ
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The categories of this paper are: solv-int
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The categories of this paper are: q-bio
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The categories of this paper are: funct-an
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The categories of this paper are: hep-ex
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The categories of this paper are: stat
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The categories of this paper are: mtrl-th
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The categories of this paper are: math
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The categories of this paper are: math-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: adap-org