Field-aligned currents in Saturn’s magnetosphere: Observations from the F-ring orbits
File(s)
Author(s)
Type
Journal Article
Abstract
We investigate the azimuthal magnetic field signatures associated with high‐latitude field‐aligned currents observed during Cassini's F‐ring orbits (October 2016–April 2017). The overall ionospheric meridional current profiles in the northern and southern hemispheres, that is, the regions poleward and equatorward of the field‐aligned currents, differ most from the 2008 observations. We discuss these differences in terms of the seasonal change between data sets and local time (LT) differences, as the 2008 data cover the nightside while the F‐ring data cover the post‐dawn and dusk sectors in the northern and southern hemispheres, respectively. The F‐ring field‐aligned currents typically have a similar four current sheet structure to those in 2008. We investigate the properties of the current sheets and show that the field‐aligned currents in a hemisphere are modulated by that hemisphere's “planetary period oscillation” (PPO) systems. We separate the PPO‐independent and PPO‐related currents in both hemispheres using their opposite symmetry. The average PPO‐independent currents peak at ~1.5 MA/rad just equatorward of the open closed field line boundary, similar to the 2008 observations. However, the PPO‐related currents in both hemispheres are reduced by ~50% to ~0.4 MA/rad. This may be evidence of reduced PPO amplitudes, similar to the previously observed weaker equatorial oscillations at similar dayside LTs. We do not detect the PPO current systems' interhemispheric component, likely a result of the weaker PPO‐related currents and their closure within the magnetosphere. We also do not detect previously proposed lower latitude discrete field‐aligned currents that act to “turn off” the PPOs.
Date Issued
2018-05-22
Date Acceptance
2018-05-03
Citation
Journal of Geophysical Research: Space Physics, 2018, 123 (5), pp.3806-3821
ISSN
2169-9402
Publisher
American Geophysical Union
Start Page
3806
End Page
3821
Journal / Book Title
Journal of Geophysical Research: Space Physics
Volume
123
Issue
5
Copyright Statement
©2018. 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.
License URL
Sponsor
Science and Technology Facilities Council (STFC)
The Royal Society
Science and Technology Facilities Council (STFC)
Grant Number
ST/N000692/1
RP140004
ST/P006922/1
Subjects
Science & Technology
Physical Sciences
Astronomy & Astrophysics
Saturn
field-aligned currents
magnetosphere
periodicities
F-ring orbits
Cassini
PLANETARY PERIOD OSCILLATIONS
POLAR IONOSPHERE
CURRENT SYSTEMS
NORTHERN
PERIODICITIES
CASSINI
MODEL
FLOW
0201 Astronomical and Space Sciences
0401 Atmospheric Sciences
Publication Status
Published
Date Publish Online
2018-05-09