Institut national de recherche scientifique français Univerité Pierre et Marie Curie Université Paris Diderot - Paris 7

Stirring Saturn’s magnetosphere with vortical winds in the upper atmosphere

Tuesday 27 September 2011, by Margaret Kivelson (UCLA)

Monday 10 October 2011 à 11h00 , Lieu : Salle de confĂ©rence du bât. 17

Electromagnetic phenomena in Saturn’s magnetosphere and ionosphere vary periodically at a period close to that of planetary rotation. Arguments relating to the slow drift of the modulation period and the inertia of different regions of Saturn’s environment require that the system be driven from regions remote from the equatorial surface, plausibly the high altitude atmosphere. The assumption that the system is driven from the ionospheric ends of the flux tubes is supported by characteristics of the magnetic perturbations observed near the magnetic equator. This presentation will describe results from a magnetohydrodynamic simulation in which the atmosphere drives vortical winds in the southern ionosphere. The wind pattern rotates about the spin axis at the modulation period of Saturn Kilometric Radiation (SKR). The simulation reproduces many features reported for magnetospheric perturbations. It also exhibits field-aligned current (FAC) patterns that correspond to properties reported for SKR emissions. In a second run of the simulation, an additional vortical flow structure is introduced into the northern high-altitude atmosphere. The northern structure rotates about the spin axis at a slightly shorter period. This second simulation provides insight into the way in which two separate frequencies affect the magnetosphere and the FACs.

Co-authors: Xianzhe Jia and Tamas Gombosi