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Title: Field-aligned currents in Saturn's southern nightside magnetosphere: Subcorotation and planetary period oscillation components
Authors: Hunt, G. J.
Cowley, Stanley W. H.
Provan, G.
Bunce, E. J.
Alexeev, I. I.
Belenkaya, E. S.
Kalegaev, V. V.
Dougherty, M. K.
Coates, A. J.
First Published: 16-Dec-2014
Publisher: American Geophysical Union (AGU)
Citation: Journal of Geophysical Research: Space Physics, 2014, 119 (12), pp. 9847–9899
Abstract: We investigate magnetic data showing the presence of field-aligned magnetosphere-ionosphere coupling currents on 31 Cassini passes across Saturn's southern postmidnight auroral region. The currents are strongly modulated in magnitude, form, and position by the phase of the southern planetary period oscillations (PPOs). PPO-independent currents are separated from PPO-related currents using the antisymmetry of the latter with respect to PPO phase. PPO-independent downward currents ~1.1 MA per radian of azimuth flow over the polar open field region indicative of significant plasma subcorotation are enhanced in an outer plasma sheet layer of elevated ionospheric conductivity carrying ~0.8 MA rad[superscript: −1] and close principally in an upward directed current sheet at ~17°–19° ionospheric colatitude carrying ~2.3 MA rad[superscript: −1] that maps to the outer hot plasma region in Saturn's magnetosphere (equatorial range ~11–16 Saturn radii (R[subscript: S])) colocated with the UV oval. Subsidiary downward and upward currents ~0.5 MA rad[superscript: −1] lie at ~19°–20.5° colatitude mapping to the inner hot plasma region, but no comparable currents are detected at larger colatitudes mapping to the cool plasma regime inside ~8 R[subscript: S]. PPO-related currents at ~17.5°–20° colatitude overlap the main upward and subsidiary downward currents and carry comparable rotating upward and downward currents peaking at ~1.7 MA rad[superscript: −1]. The overall current layer colatitude is also modulated with 1° amplitude in the PPO cycle, maximum equatorward adjacent to the peak upward PPO current and maximum poleward adjacent to peak downward PPO current. This phasing requires the current system to be driven from the planetary atmosphere rather than directly from the magnetosphere.
DOI Link: 10.1002/2014JA020506
ISSN: 2169-9402
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © 2014, 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.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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