Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Fine structure of flare ribbons and evolution of electric currents   Emission of solar flares across the electromagnetic spectrum is often
observed in the form of two expanding ribbons. The standard flare model
explains the flare ribbons as footpoints of magnetic arcades, emitting due to
interaction of energetic particles with the chromospheric plasma. However, the
physics of this interaction and properties of the accelerated particles are
still unknown. We present results of multiwavelength observations of C2.1 flare
of August 15, 2013, observed with New Solar Telescope (NST) of Big Bear Solar
Observatory, Solar Dynamics Observatory (SDO), GOES and FERMI spacecraft. The
observations reveal previously unresolved sub-arcsecond structure of the flare
ribbons in regions of strong magnetic field consisting from numerous
small-scale bright knots. We observe red-blue asymmetry of H alpha flare
ribbons with a width as small as 100 km. We discuss the relationship between
the ribbons and vertical electric currents estimated from vector magnetograms,
and show that Joule heating can be responsible for energization of H alpha
knots in the ribbons.

21
The categories of this paper are: adap-org
14
The categories of this paper are: math-ph
20
The categories of this paper are: acc-phys
10
The categories of this paper are: q-bio
15
The categories of this paper are: nucl-ex
26
The categories of this paper are: bayes-an
4
The categories of this paper are: cond-mat
28
The categories of this paper are: alg-geom
30
The categories of this paper are: q-alg
3
The categories of this paper are: physics
35
The categories of this paper are: mtrl-th
7
The categories of this paper are: hep-th
9
The categories of this paper are: nlin
37
The categories of this paper are: supr-con
0
The categories of this paper are: hep-ph
12
The categories of this paper are: nucl-th