Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Magnetic Cloud and Sheath in the Ground-Level Enhancement Event of 2000
  July 14. II. Effects on the Forbush Decrease   Forbush decreases (Fds) in galactic cosmic ray intensity are related to
interplanetary coronal mass ejections (ICMEs). The parallel diffusion of
particles is reduced because the magnetic turbulence level in sheath region
bounded by ICME's leading edge and shock is high. Besides, in sheath and
magnetic cloud (MC) energetic particles would feel enhanced magnetic focusing
effect caused by the strong inhomogeneity of the background magnetic field.
Therefore, particles would be partially blocked in sheath-MC structure. Here,
we study two-step Fds by considering the magnetic turbulence and background
magnetic field in sheath-MC structure with diffusion coefficients calculated
with theoretical models, to reproduce the Fd associated with the ground-level
enhancement event on 2000 July 14 by solving the focused transport equation.
The sheath and MC are set to spherical caps that are portions of spherical
shells with enhanced background magnetic field. Besides, the magnetic
turbulence levels in sheath and MC are set to higher and lower than that in
ambient solar wind, respectively. In general, the simulation result conforms to
the main characteristics of the Fd observation, such as the pre-increase
precursor, amplitude, total recovery time, and the two-step decrease of the
flux at the arrival of sheath and MC. It is suggested that sheath played an
important role in the amplitude of Fd while MC contributed to the formation of
the second step decrease and prolonged the recovery time. It is also inferred
that both magnetic turbulence and background magnetic field in sheath-MC
structure are important for reproducing the observed two-step Fd.

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The categories of this paper are: cond-mat
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The categories of this paper are: q-alg
34
The categories of this paper are: chem-ph
29
The categories of this paper are: funct-an
33
The categories of this paper are: plasm-ph
15
The categories of this paper are: nucl-ex
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The categories of this paper are: q-bio
32
The categories of this paper are: atom-ph
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The categories of this paper are: hep-ph
28
The categories of this paper are: alg-geom
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The categories of this paper are: cs
20
The categories of this paper are: acc-phys
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The categories of this paper are: comp-gas
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The categories of this paper are: gr-qc
35
The categories of this paper are: mtrl-th
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The categories of this paper are: econ