Driving Saturn's Magnetospheric Periodicities from the Upper Atmosphere/Ionosphere: Magnetotail Response to Dual Sources
Abstract
Despite the high degree of axial symmetry of Saturn's internal magnetic field, rotation-associated periodicities are evident in Saturn's electromagnetic radiation, its magnetic perturbations and its particle populations. Although close to the mean rotation period of the cloud tops, the electromagnetic period drifts slightly over a time scale of years and, at high latitudes, differs in the north and south. The source of the periodicity remains a mystery. As an extension of an earlier model of Saturn's rotational periodicity [Jia et al., 2012, JGR, A04215], the model investigated here places the momentum source in the upper atmosphere/ionosphere with the wind patterns in both hemispheres rotating about the spin axis at different rates typical of the 2005-2006 southern summer for which Cassini data have been extensively analyzed. A source at low altitudes would account for the persistence of phase following solar wind disruption of magnetospheric flow patterns but might not produce appropriate magnetospheric responses. However, using a 3D magnetohydrodynamic simulation in which vortical winds in the ionosphere drive field-aligned currents into the magnetosphere, we show that the dual sources account nearly quantitatively for many measured magnetospheric responses. This paper focuses on the magnetotail where the model is shown to reproduce many well-documented results of data analysis including the features that appear distinctly at each of the two periods and those that appear as a carrier signal with amplitude modulation and phase shifts. In particular, the model accounts for current sheet flapping and modulation of the plasma sheet thickness and for the periodic structure of density enhancements at high latitudes at different periods in the north and the south.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMSM51B2305J
- Keywords:
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- 2431 IONOSPHERE / Ionosphere/magnetosphere interactions;
- 5737 PLANETARY SCIENCES: FLUID PLANETS / Magnetospheres;
- 6275 PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS / Saturn;
- 7899 SPACE PLASMA PHYSICS / General or miscellaneous