Provan_et_al-2013-Journal_of_Geophysical_Research-_Space_Physics.pdf (2.49 MB)
Planetary period magnetic field oscillations in Saturn's magnetosphere: Postequinox abrupt nonmonotonic transitions to northern system dominance
journal contribution
posted on 2016-12-16, 11:21 authored by G. Provan, S. W. H. Cowley, J. Sandhu, D. J. Andrews, M. K. DoughertyWe examine the “planetary period” magnetic field oscillations observed in the “core”
region of Saturn’s magnetosphere (dipole L ≤ 12), on 56 near-equatorial Cassini periapsis
passes that took place between vernal equinox in August 2009 and November 2012.
Previous studies have shown that these consist of the sum of two oscillations related to the
northern and southern polar regions having differing amplitudes and periods that had
reached near-equal amplitudes and near-converged periods ~10.68 h in the interval to
~1 year after equinox. The present analysis shows that an interval of strongly differing
behavior then began ~1.5 years after equinox, in which abrupt changes in properties took
place at ~6- to 8-month intervals, with three clear transitions occurring in February 2011,
August 2011, and April 2012, respectively. These are characterized by large simultaneous
changes in the amplitudes of the two systems, together with small changes in period about
otherwise near-constant values of ~10.63 h for the northern system and ~10.69 h for the
southern (thus, not reversed postequinox) and on occasion jumps in phase. The first
transition produced a resumption of strong southern system dominance unexpected under
northern spring conditions, while the second introduced comparably strong northern
system dominance for the first time in these data. The third resulted in suppression of all
core oscillations followed by re-emergence of both systems on a time scale of ~85 days,
with the northern system remaining dominant but not as strongly as before. This behavior
poses interesting questions for presently proposed theoretical scenarios.
Funding
Work at Leicester was supported by STFC grant ST/H002480/1.
History
Citation
Journal of Geophysical Research: Space Physics, 2013, 118 (6), pp. 3243-3264 (22)Author affiliation
/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and AstronomyVersion
- VoR (Version of Record)
Published in
Journal of Geophysical Research: Space PhysicsPublisher
American Geophysical Union (AGU), Wileyissn
2169-9402;2169-9402Acceptance date
2013-02-12Available date
2016-12-16Publisher DOI
Publisher version
http://onlinelibrary.wiley.com/doi/10.1002/jgra.50186/abstractLanguage
enAdministrator link
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