Modeling a Rotating Partial Ring Current in the Saturn's Magnetosphere as a Source of B-field Periodicities: A Progress Report

Details Modeling a Rotating Partial Ring Current in the Saturn's Magnetosphere as a Source of B-field Periodicities: A Progress Report Modeling a Rotating Partial Ring Current in the Saturn's Magnetosphere as a Source of B-field Periodicities: A Progress Report

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm31c..05t&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SM31C-05

Physics

[2740] Magnetospheric Physics / Magnetospheric Configuration And Dynamics, [2756] Magnetospheric Physics / Planetary Magnetospheres, [6275] Planetary Sciences: Solar System Objects / Saturn

Scientific paper

Saturn's magnetic dipole axis is almost perfectly aligned with its rotation axis and thus one would expect no diurnal effects in the Kronian magnetosphere. It was therefore surprising to find periodic phenomena in almost all of the magnetospheric measurements, but a lack of longitudinal asymmetry to account for those phenomena. The Saturn Kilometric Radiation (SKR) was the first remotely observed phenomenon to show clear periodicities, which was used to define a rotational period of the planet, in a similar way that had been done for Jupiter. However, the SKR-derived period later changed by several minutes, which directly tells us that SKR is only loosely related to the rotation period of the planet and is a magnetospheric and/or ionospheric phenomenon. Cassini measurements have now revealed periodic modulations close to the SKR-derived period in the magnetic field, energetic particles, energetic neutral atoms (ENA), and more. Any hypothesis attempting to explain the origin of the periodic behavior must be able to explain how the planetary rotation propagates out to the largely subcorotating magnetosphere, and to explain the mechanisms that relate the periodic modulations in the different measurements. In order to explore the global current system of Saturn and its relation to periodicities, we are constructing a flexible rotating PRC module, based on the pressure of the injected hot plasma and an empirical model of the background B-field, constructed from many years of Cassini's magnetometer data. In the reported phase of this ongoing research, we describe a computational procedure to derive electric currents induced by the injected hot plasma, and a fast Biot-Savart calculation of the field perturbation due to the PRC. The obtained results will be compared with Cassini magnetic field observations. Using the model, we investigate the relation between the periodic magnetic field perturbations observed from Cassini and the rotating 3D current system, driven by periodically injected energetic (>2 keV) particles that form a partial ring current (PRC) co-rotating with the planet. Plasma pressures inferred from the Cassini Plasma Spectrometer (CAPS) (<2 keV) and the Magnetospheric Imaging Instrument (MIMI) (>2 keV) will be used to compute the currents and their associated magnetic field perturbations. The distribution of the "hot" (>2 keV)plasma pressure is derived from Energetic Neutral Atom (ENA) images, obtained by the Ion Neutral Camera (INCA) and in-situ spectral measurements.

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