Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Statistical Study of Photospheric Magnetic Field Changes During 75
  Solar Flares   Abrupt and permanent changes of photospheric magnetic fields have been
observed during solar flares. The changes seem to be linked to the
reconfiguration of magnetic fields, but their origin is still unclear. We
carried out a statistical analysis of permanent line-of-sight magnetic field
($B_{\rm LOS}$) changes during 18 X-, 37 M-, 19 C- and 1 B-class flares using
data from Solar Dynamics Observatory/Helioseismic and Magnetic Imager. We
investigated the properties of permanent changes, such as frequency, areas, and
locations. We detected changes of $B_{\rm LOS}$ in 59/75 flares. We find that
strong flares are more likely to show changes, with all flares $\ge$ M1.6
exhibiting them. For weaker flares, permanent changes are observed in 6/17
C-flares. 34.3\% of the permanent changes occurred in the penumbra and 18.9\%
in the umbra. Parts of the penumbra appeared or disappeared in 23/75 flares.
The area where permanent changes occur is larger for stronger flares. Strong
flares also show a larger change of flux, but there is no dependence of the
magnetic flux change on the heliocentric angle. The mean rate of change of
flare-related magnetic field changes is 20.7 Mx cm$^{-2}$ min$^{-1}$. The
number of permanent changes decays exponentially with distance from the
polarity inversion line. The frequency of the strength of permanent changes
decreases exponentially, and permanent changes up to 750 Mx cm$^{-2}$ were
observed. We conclude that permanent magnetic field changes are a common
phenomenon during flares, and future studies will clarify their relation to
accelerated electrons, white light emission, and sunquakes to further
investigate their origin.

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The categories of this paper are: ao-sci
13
The categories of this paper are: quant-ph
0
The categories of this paper are: hep-ph
3
The categories of this paper are: physics
2
The categories of this paper are: math
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The categories of this paper are: dg-ga
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The categories of this paper are: math-ph
9
The categories of this paper are: nlin
28
The categories of this paper are: alg-geom
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The categories of this paper are: nucl-ex
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The categories of this paper are: funct-an
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The categories of this paper are: stat
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The categories of this paper are: atom-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: comp-gas
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The categories of this paper are: nucl-th