Field-aligned currents in Saturn's magnetosphere: local time dependence of southern summer currents in the dawn sector between midnight and noon
File(s)
Author(s)
Type
Journal Article
Abstract
We examine and compare the magnetic field perturbations associated with field-aligned ionosphere-magnetosphere coupling currents at Saturn, observed by the Cassini spacecraft during two sequences of highly inclined orbits in 2006/2007 and 2008 under late southern summer conditions. These sequences explore the southern currents in the dawn-noon and midnight sectors, respectively, thus allowing investigation of possible origins of the local time (LT) asymmetry in auroral Saturn kilometric radiation (SKR) emissions, which peak in power at ~8 h LT in the dawn-noon sector. We first show that the dawn-noon field data generally have the same four-sheet current structure as found previously in the midnight data and that both are similarly modulated by “planetary period oscillation” (PPO) currents. We then separate the averaged PPO-independent (e.g., subcorotation) and PPO-related currents for both LT sectors by using the current system symmetry properties. Surprisingly, we find that the PPO-independent currents are essentially identical within uncertainties in the dawn-dusk and midnight sectors, thus providing no explanation for the LT dependence of the SKR emissions. The main PPO-related currents are, however, found to be slightly stronger and narrower in latitudinal width at dawn-noon than at midnight, leading to estimated precipitating electron powers, and hence emissions, that are on average a factor of ~1.3 larger at dawn-noon than at midnight, inadequate to account for the observed LT asymmetry in SKR power by a factor of ~2.7. Some other factors must also be involved, such as a LT asymmetry in the hot magnetospheric auroral source electron population.
Date Issued
2016-08-06
Date Acceptance
2016-07-30
Citation
Journal of Geophysical Research: Space Physics, 2016, 121 (8), pp.7785-7804
ISSN
2169-9402
Publisher
American Geophysical Union
Start Page
7785
End Page
7804
Journal / Book Title
Journal of Geophysical Research: Space Physics
Volume
121
Issue
8
Copyright Statement
© 2016 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.
Sponsor
Imperial College Trust
Science and Technology Facilities Council (STFC)
The Royal Society
Science and Technology Facilities Council (STFC)
Science and Technology Facilities Council
Identifier
http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000385811500033&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=1ba7043ffcc86c417c072aa74d649202
Grant Number
N/A
ST/K001051/1
RP140004
ST/N000692/1
ST/N002776/1
Subjects
Science & Technology
Physical Sciences
Astronomy & Astrophysics
AURORAL OVAL
POLAR IONOSPHERE
CURRENT SYSTEMS
NORTHERN
CASSINI
BOUNDARY
FLOWS
MODEL
HST
Publication Status
Published