Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Real-time imaging of density ducts between the plasmasphere and
  ionosphere   Ionization of the Earth's atmosphere by sunlight forms a complex,
multi-layered plasma environment within the Earth's magnetosphere, the
innermost layers being the ionosphere and plasmasphere. The plasmasphere is
believed to be embedded with cylindrical density structures (ducts) aligned
along the Earth's magnetic field, but direct evidence for these remains scarce.
Here we report the first direct wide-angle observation of an extensive array of
field-aligned ducts bridging the upper ionosphere and inner plasmasphere, using
a novel ground-based imaging technique. We establish their heights and motions
by feature-tracking and parallax analysis. The structures are strikingly
organized, appearing as regularly-spaced, alternating tubes of overdensities
and underdensities strongly aligned with the Earth's magnetic field. These
findings represent the first direct visual evidence for the existence of such
structures.

1
The categories of this paper are: cs
37
The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
34
The categories of this paper are: chem-ph
21
The categories of this paper are: adap-org
12
The categories of this paper are: nucl-th
5
The categories of this paper are: gr-qc
27
The categories of this paper are: comp-gas
18
The categories of this paper are: econ
17
The categories of this paper are: q-fin
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
33
The categories of this paper are: plasm-ph
24
The categories of this paper are: dg-ga
19
The categories of this paper are: eess