Physics @ Berkeley
Events in Physics
Title: "Global dynamics of the Jovian magnetosphere"    (Colloquia)
Start Date: 10/18/2004
Time: 4:30 pm
Location: 1 LeConte Hall
Speaker: Margaret Kivelson
Affiliation: Dept of Earth & Space Sciences, UCLA
Contact Person: K. Lee   (510) 642-3034
Details: The global scale structure of the Jovian magnetosphere has been documented by data from seven spacecraft whose collective passes cover all local times, mainly in the near-equatorial region. As contrasted with Earth’s magnetosphere, where the day-night asymmetry dominates the local time variation of structure, the Jovian magnetosphere also reveals strong dawn-dusk asymmetries. Those asymmetries illuminate the effects of plasma rotation in the presence of externally imposed forces at the magnetopause. Analysis of the system leads to a description of the physical processes that produce the asymmetry and gives insight into unique aspects of the plasma transport in a magnetosphere dominated by rotation. The most dynamic portion of the magnetosphere is the plasma disk. At some local times, its outer edge is marginally stable and at others strongly unstable. The most unstable sector is localized on the night side, where an outflow of material down tail thins the plasma disk. The same outflow evacuates portions of the flux tubes, causing the outer portions to break off and leave closed depleted flux tubes behind. As the depleted flux tubes move on to the dayside at large radial distance on the morning side, they form a distinct plasma/magnetic regime. The residual sheet thickens as flux tubes rotate to noon. During this rotation, there is some evidence of weak loss of plasma. A massive change takes place in the afternoon sector where the sheet energizes and thickens as it moves from noon to dusk and assimilates the empty flux tubes of the outer magnetosphere. It is probable that this assimilation is accomplished through a short perpendicular scale centrifugally driven ballooning leading to Bohm diffusion of plasma to refill the previously emptied tubes. The well-known dawn dusk asymmetry in the UV aurora (refs) is very likely associated with the vastly larger tapping of the ionospheric "flywheel" in the afternoon sector that the model proposes.

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