Dual periodicities in the magnetospheres of Jupiter and Saturn

Details Dual periodicities in the magnetospheres of Jupiter and Saturn Dual periodicities in the magnetospheres of Jupiter and Saturn

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p53c..08c&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #P53C-08

Physics

[2756] Magnetospheric Physics / Planetary Magnetospheres, [5734] Planetary Sciences: Fluid Planets / Magnetic Fields And Magnetism, [6275] Planetary Sciences: Solar System Objects / Saturn

Scientific paper

Two distinct periods, both near the rotational period of the planet, have been identified in Saturn’s kilometric radio emissions [Kurth et al., 2008, Gurnett et al., 2009]. The first is that of the usual SLS rotation rate, associated with a wide range of periodic phenomena in Saturn’s magnetosphere. The amplitude of the second period, at 815 deg/day (10.6 hours) or approximately 2% faster than SLS, is typically lower than that of the SLS period’s amplitude. Unlike the SLS period, the 815 deg/day signal may have a constant rate. Gurnett et al., 2009 showed that radio emissions modulated at the 815 deg/day rate are produced in the northern hemisphere, while those at the SLS rate are produced in the southern hemisphere. We note that Jupiter’s magnetosphere also exhibits two distinct periods. One (the System III period) corresponds to the rotation rate of the planet’s interior. The second, “System IV” periodicity is 2-3% slower than System III and has been reported at rates which vary by ~1%, and has been observed to abruptly shift in phase by 100o [Brown, 1995.] We suggest that these dual periodicities in the magnetospheres of Jupiter and Saturn are related. One period is generated by asymmetries in the planet’s internal field, and therefore reflects the internal rotation rate of the planet. In the case of Jupiter, this is the System III period; in the case of Saturn, this would be the 815 deg/day period. In the case of Saturn, the relatively low amplitude of this period result the highly symmetric nature of Saturn’s internal field. The northern hemisphere source for radio emissions with this periodicity suggests that the asymmetries in Saturn’s internal field are primarily in the north. The second, slower type of periodicity, at both Jupiter and Saturn, may reflect the rotation rate of the thermosphere, it would not be expected to be constant. Seasonal changes and magnetospheric forcing could plausibly cause variability over the course of months and years.

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