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Title: Planetary period oscillations in Saturn's magnetosphere: Evidence in magnetic field phase data for rotational modulation of Saturn kilometric radiation emissions
Authors: Andrews, D. J.
Cowley, S. W. H.
Provan, G.
Cecconi, B.
Lamy, L.
Zarka, P.
Dougherty, M. K.
First Published: 10-Sep-2011
Publisher: American Geophysical Union (AGU); Wiley
Citation: Journal of Geophysical Research A: SPACE PHYSICS, 2011, 116 (9)
Abstract: [1] Initial Voyager observations of Saturn kilometric radiation (SKR) indicated that the modulations in emitted power near the ∼11 h planetary rotation period are “strobe like,” varying with a phase independent of observer position, while subsequent Cassini studies of related oscillations in the magnetospheric magnetic field and plasma parameters have shown that these rotate around the planet with a period close to the SKR period. However, analysis of magnetic oscillation data over the interval 2004–2010 reveals the presence of variable secular drifts between the phases of the dominant southern period magnetic oscillations and SKR modulations, which become very marked after Cassini apoapsis moved for the first time into the postdusk sector in mid-2009. Here we use a simple theoretical model to show that such phase drifts arise if the SKR modulation phase also rotates around the auroral oval, combined with a highly restricted view of the SKR sources by the spacecraft due to the conical beaming of the emissions. Strobe-like behavior then occurs in the predawn-to-noon sector where the spacecraft has a near-continuous view of the most intense midmorning SKR sources, in agreement with the Voyager findings, while elsewhere the SKR modulation phase depends strongly on spacecraft local time, being in approximate antiphase with the midmorning sources in the postdusk sector. Supporting evidence for this scenario is provided through an independent determination of the variable rotation period of the southern magnetic field perturbations throughout the 6 year interval.
DOI Link: 10.1029/2011JA016636
ISSN: 0148-0227
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © 2011 by the American Geophysical Union. All rights reserved. Archived with reference to Usage Permissions granted to authors, available at
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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