Magnetospheric Storms at Saturn

Details Magnetospheric Storms at Saturn Magnetospheric Storms at Saturn

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.p43a0953b&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #P43A-0953

Other

2740 Magnetospheric Configuration And Dynamics, 2756 Planetary Magnetospheres (5443, 5737, 6033), 2778 Ring Current, 2784 Solar Wind/Magnetosphere Interactions, 2788 Magnetic Storms And Substorms (7954)

Scientific paper

The Ion and Neutral Camera (INCA) on board the Cassini mission images magnetospheric proton and O+ distributions in the ~10-300 keV range in the Saturnian magnetosphere. The most outstanding feature of the global energetic ion distributions is the occurrence of gradual increases (~1 d) on the nightside of Saturn, followed by corotation lasting several days of a localized distribution. We have studied the interplanetary magnetic field (IMF) obtained from the Cassini Magnetic Field Experiment (MFE), and solar wind speed obtained from the Cassini Charge Energy Mass Spectrometer (CHEMS), when Cassini was outside the magnetosphere. Through comparisons with the dynamics and morphology of the global energetic ion distributions obtained by INCA images, we find a behavior that resembles the global behavior of the terrestrial ring current during geomagnetic storms observed by the High Energy Neutral Atom imager on board the IMAGE mission: Gradual increases on the nightside at Saturn appear to be related to conditions that lead to high convection (northward IMF and high solar-wind speed) - the storm mainphase. At Earth, such periods correspond to strong magnetospheric convection and a small Alfven layer, so that hot plasma is convected from the tail sunward to the nightside, where particle distributions reach their highest intensity (partial ring current). The sudden transition to a localized distribution corotating with a period about the same as the periodicity determined from Saturn Kilometric Radiation (SKR) measurements, appears to be related to changes in the solar wind leading to decreased convection (southward IMF and lower solar wind speed) - the storm recovery phase. At Earth, such periods correspond to weak magnetospheric convection and a larger Alfven layer enclosing the previously convection-dominated plasma so that the region becomes dominated by magnetic drifts (corotation dominated at Saturn). We study two periods, 2-4 December, 2004 and 2-7 January, 2005, and investigate what the similarities and differences to global signatures of terrestrial storms are. We will put our results into context with similar studies of solar wind driving of auroral activity on Saturn ( Cowley, Bunce, Crary and others), which advocate that magnetospheric activity at Saturn is mostly controlled by solar wind pressure and less by the polarity of the IMF.

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