The magnetospheric clock of Saturn-A self-organized plasma dynamo
2013 (English)In: Physics of Plasmas, ISSN 1070-664X, Vol. 20, no 8, 082901- p.Article in journal (Refereed) Published
The plasma in the inner magnetosphere of Saturn is characterized by large-amplitude azimuthal density variations in the equatorial plane, with approximately a sinusoidal dependence on the azimuthal angle [D. A. Gurnett et al., Science 316, 442 (2007)]. This structure rotates with close to the period of the planet itself and has been proposed to steer other nonaxisymmetric phenomena, e. g., the Saturn kilometric radiation SKR [W. S. Kurth et al., Geophys. Res. Lett. 34, L02201 (2007)], and inner-magnetosphere magnetic field perturbations [D. J. Southwood and M. G. Kivelson, J. Geophys. Res. 112(A12), A12222 (2007)]. There is today no consensus regarding the basic driving mechanism. We here propose it to be a plasma dynamo, located in the neutral gas torus of Enceladus but coupled both inwards, through electric currents along the magnetic field lines down to the planet, and outwards through the plasma flow pattern there. Such a dynamo mechanism is shown to self-regulate towards a state that, with realistic parameters, can reproduce the observed configuration of the magnetosphere. This state is characterized by three quantities: the Pedersen conductivity in the polar cap, the ionization time constant in the neutral gas torus, and a parameter characterizing the plasma flow pattern. A particularly interesting property of the dynamo is that regular (i.e., constant-amplitude, sinusoidal) variations in the last parameter can lead to complicated, non-periodic, oscillations around the steady-state configuration.
Place, publisher, year, edition, pages
2013. Vol. 20, no 8, 082901- p.
IdentifiersURN: urn:nbn:se:kth:diva-129471DOI: 10.1063/1.4816669ISI: 000323946800076OAI: oai:DiVA.org:kth-129471DiVA: diva2:653609
QC 201310042013-10-042013-09-302013-10-04Bibliographically approved