Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Comparing magnetic field extrapolations with measurements of magnetic
  loops   We compare magnetic field extrapolations from a photospheric magnetogram with
the observationally inferred structure of magnetic loops in a newly developed
active region. This is the first time that the reconstructed 3D-topology of the
magnetic field is available to test the extrapolations. We compare the
observations with potential fields, linear force-free fields and non-linear
force-free fields. This comparison reveals that a potential field extrapolation
is not suitable for a reconstruction of the magnetic field in this young,
developing active region. The inclusion of field-line-parallel electric
currents, the so called force-free approach, gives much better results.
Furthermore, a non-linear force-free computation reproduces the observations
better than the linear force-free approximation, although no free parameters
are available in the former case.

12
The categories of this paper are: nucl-th
30
The categories of this paper are: q-alg
34
The categories of this paper are: chem-ph
27
The categories of this paper are: comp-gas
2
The categories of this paper are: math
9
The categories of this paper are: nlin
21
The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex
18
The categories of this paper are: econ
25
The categories of this paper are: patt-sol
7
The categories of this paper are: hep-th
23
The categories of this paper are: solv-int
14
The categories of this paper are: math-ph
32
The categories of this paper are: atom-ph
16
The categories of this paper are: stat
5
The categories of this paper are: gr-qc