Field-aligned currents in Saturn's northern nightside magnetosphere: Evidence for interhemispheric current flow associated with planetary period oscillations
File(s)
Author(s)
Type
Journal Article
Abstract
We investigate the magnetic perturbations associated with field-aligned currents observed on 34 Cassini passes over the premidnight northern auroral region during 2008. These are found to be significantly modulated not only by the northern planetary-period oscillation (PPO) system, similar to the southern currents by the southern PPO system found previously, but also by the southern PPO system as well, thus providing the first clear evidence of PPO-related interhemispheric current flow. The principal field-aligned currents of the two PPO systems are found to be co-located in northern ionospheric colatitude, together with the currents of the PPO-independent (subcorotation) system, located between the vicinity of the open-closed field boundary and field lines mapping to ~9 Saturn radius (Rs) in the equatorial plane. All three systems are of comparable magnitude, ~3 MA in each PPO half-cycle. Smaller PPO-related field-aligned currents of opposite polarity also flow in the interior region, mapping between ~6 and ~9 Rs in the equatorial plane, carrying a current of ~ ±2 MA per half-cycle, which significantly reduce the oscillation amplitudes in the interior region. Within this interior region the amplitudes of the northern and southern oscillations are found to fall continuously with distance along the field lines from the corresponding hemisphere, thus showing the presence of cross-field currents, with the southern oscillations being dominant in the south, and modestly lower in amplitude than the northern oscillations in the north. As in previous studies, no oscillations related to the opposite hemisphere are found on open field lines in either hemisphere.
Date Issued
2015-09-26
Date Acceptance
2015-08-23
Citation
Journal of Geophysical Research: Space Physics, 2015, 120 (9), pp.7552-7584
ISSN
2169-9402
Publisher
American Geophysical Union
Start Page
7552
End Page
7584
Journal / Book Title
Journal of Geophysical Research: Space Physics
Volume
120
Issue
9
Copyright Statement
© 2015 The Authors.
This is an open access article under the
terms of the Creative Commons
Attribution License, which permits use,
distribution and reproduction in any
medium, provided the original work is
properly cited.
This is an open access article under the
terms of the Creative Commons
Attribution License, which permits use,
distribution and reproduction in any
medium, provided the original work is
properly cited.
License URL
Sponsor
Science and Technology Facilities Council (STFC)
The Royal Society
Science and Technology Facilities Council
Grant Number
ST/K001051/1
RP140004
ST/N002776/1
Subjects
Science & Technology
Physical Sciences
Astronomy & Astrophysics
Saturn
field-aligned currents
magnetosphere
aurora
periodicity
ionosphere
MAGNETIC-FIELD
ROTATION PERIOD
CURRENT SYSTEMS
AURORAL OVAL
PLASMA FLOWS
SOLAR-WIND
IONOSPHERE
PERIODICITIES
PERTURBATIONS
DEPENDENCE
Publication Status
Published