Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Filament Shape Versus Coronal Potential Magnetic Field Structure   Solar filament shape in projection on disc depends on the structure of the
coronal magnetic field. We calculate the position of polarity inversion lines
(PILs) of coronal potential magnetic field at different heights above the
photosphere, which compose the magnetic neutral surface, and compare with them
the distribution of the filament material in H$\alpha$ chromospheric images. We
found that the most of the filament material is enclosed between two polarity
inversion lines (PILs), one at a lower height close to the chromosphere and one
at a higher level, which can be considered as a height of the filament spine.
Observations of the same filament on the limb by the {\it STEREO} spacecraft
confirm that the height of the spine is really very close to the value obtained
from the PIL and filament border matching. Such matching can be used for
filament height estimations in on-disk observations. Filament barbs are housed
within protruding sections of the low-level PIL. On the base of simple model,
we show that the similarity of the neutral surfaces in potential and
non-potential fields with the same sub-photospheric sources is the reason for
the found tendency for the filament material to gather near the potential-field
neutral surface.

3
The categories of this paper are: physics
9
The categories of this paper are: nlin
8
The categories of this paper are: hep-ex
23
The categories of this paper are: solv-int
18
The categories of this paper are: econ
35
The categories of this paper are: mtrl-th
4
The categories of this paper are: cond-mat
15
The categories of this paper are: nucl-ex
1
The categories of this paper are: cs
37
The categories of this paper are: supr-con
25
The categories of this paper are: patt-sol
2
The categories of this paper are: math
0
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: q-fin
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The categories of this paper are: eess