Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: High-altitude signatures of ionospheric density depletions caused by
  field-aligned currents   We present Cluster measurements of large electric fields correlated with
intense downward field-aligned currents, and show that the data can be
reproduced by a simple model of ionospheric plasma depletion caused by the
currents. This type of magnetosphere-ionosphere interaction may be important
when considering the mapping between these two regions of space.

7
The categories of this paper are: hep-th
20
The categories of this paper are: acc-phys
25
The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn
35
The categories of this paper are: mtrl-th
23
The categories of this paper are: solv-int
0
The categories of this paper are: hep-ph
17
The categories of this paper are: q-fin
33
The categories of this paper are: plasm-ph
10
The categories of this paper are: q-bio
15
The categories of this paper are: nucl-ex
2
The categories of this paper are: math
16
The categories of this paper are: stat
19
The categories of this paper are: eess
30
The categories of this paper are: q-alg
26
The categories of this paper are: bayes-an