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Titel |
Planetary period oscillations in Saturn's magnetosphere: comments on the relation between post-equinox periods determined from magnetic field and SKR emission data |
VerfasserIn |
S. W. H. Cowley, G. Provan |
Medientyp |
Artikel
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Sprache |
Englisch
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ISSN |
0992-7689
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Digitales Dokument |
URL |
Erschienen |
In: Annales Geophysicae ; 33, no. 7 ; Nr. 33, no. 7 (2015-07-24), S.901-912 |
Datensatznummer |
250121224
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Publikation (Nr.) |
copernicus.org/angeo-33-901-2015.pdf |
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Zusammenfassung |
We discuss the properties of Saturn planetary period
oscillations (PPOs) deduced from analysis of Saturn kilometric radiation
(SKR) modulations by Fischer et al. (2014), and
from prior analysis of magnetic field oscillations data by Andrews et al. (2012) and Provan
et al. (2013), with emphasis
on the post-equinox interval from early 2010 to early 2013. Fischer et
al. (2014)
characterize this interval as showing single phase-locked periods in the
northern and southern SKR modulations observed in polarization-separated
data, while the magnetic data generally show the presence of separated dual
periods, northern remaining shorter than southern. We show that the single
SKR period corresponds to the southern magnetic period early in 2010, segues
into the northern period in late 2010, and returns to the southern period in
mid-2012, approximately in line with changes in the dominant magnetic
oscillation. An exception occurs in mid-February to late August 2011 when
two periods are again discerned in SKR data, in good agreement with the
ongoing dual periods in the magnetic data. Fischer et al. (2014) discuss this
change in terms of a large jump in the southern SKR period related to the
Great White Spot storm, which the magnetic data show is primarily due
instead to a reappearance in the SKR data of the ongoing southern
modulation in a transitory interval of resumed southern dominance. In the
earlier interval from early April 2010 to mid-February 2011 when Fischer et
al. (2014) deduce single phase-locked periods, we show unequivocal evidence in the
magnetic data for the presence of separated dual oscillations of
approximately equal amplitude. We suggest that the apparent single SKR
periods result from a previously reported phenomenon in which modulations
associated with one hemisphere appear in polarization-separated data
associated with the other. In the following interval, mid-August 2011 to
early April 2012, when Fischer et al. (2014) again report phase-locked northern and
southern oscillations, no ongoing southern oscillation of separate period
is discerned in the magnetic data. However, the magnetic amplitude data show
that if a phase-locked southern oscillation is indeed present, its amplitude
must be less than ~ 5–10 % of the northern oscillation. |
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