Field-aligned currents in Saturn's nightside magnetosphere: subcorotation and planetary period oscillation components during northern spring
File(s)Bradley et al (JGR published May 2018).pdf (17.64 MB)
Published version
Author(s)
Type
Journal Article
Abstract
We newly analyze Cassini magnetic field data from the 2012/2013 Saturn northern spring interval of highly inclined orbits and compare them with similar data from late southern summer in 2008, thus providing unique information on the seasonality of the currents that couple momentum between Saturn's ionosphere and magnetosphere. Inferred meridional ionospheric currents in both cases consist of a steady component related to plasma subcorotation, together with the rotating current systems of the northern and southern planetary period oscillations (PPOs). Subcorotation currents during the two intervals show opposite north‐south polar region asymmetries, with strong equatorward currents flowing in the summer hemispheres but only weak currents flowing to within a few degrees of the open‐closed boundary (OCB) in the winter hemispheres, inferred due to weak polar ionospheric conductivities. Currents peak at ~1 MA rad−1 in both hemispheres just equatorward of the open‐closed boundary, associated with total downward polar currents ~6 MA, then fall across the narrow auroral upward current region to small values at subauroral latitudes. PPO‐related currents have a similar form in both summer and winter with principal upward and downward field‐aligned currents peaking at ~1.25 MA rad−1 being essentially collocated with the auroral upward current and approximately equal in strength. Though northern and southern PPO currents were approximately equal during both intervals, the currents in both hemispheres were dual modulated by both systems during 2012/2013, with approximately half the main current closing in the opposite ionosphere and half cross field in the magnetosphere, while only the northern hemisphere currents were similarly dual modulated in 2008.
Date Issued
2018-05-01
Date Acceptance
2018-04-04
Citation
Journal of Geophysical Research: Space Physics, 2018, 123 (5), pp.3602-3636
ISSN
2169-9380
Publisher
American Geophysical Union
Start Page
3602
End Page
3636
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 (https://creativecommons.org/licenses/by/4.0/), which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Identifier
http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000435943300023&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=1ba7043ffcc86c417c072aa74d649202
Subjects
Science & Technology
Physical Sciences
Astronomy & Astrophysics
AURORAL OVAL
POLAR IONOSPHERE
CURRENT SYSTEMS
MAGNETIC-FIELD
SOLAR-WIND
CASSINI
MODEL
PERIODICITIES
COROTATION
DEPENDENCE
Publication Status
Published
Date Publish Online
2018-05-11