Space Science Seminar: Some current problems in magnetospheric MHD

Professor David Southwood, Imperial College London.

Wednesday 10 December 2014, 0930-1030
Lecture Theatre 6, Management School Building

In this seminar Professor Southwood will tackle some outstanding problems at the cutting edge of space plasma physics research. Topics include: Electromagnetism of Saturn's rings; Is the Saturn magnetosphere good model of a pulsar?; and Alfvén waves and MHD instability/reconnection.

1. Electromagnetism of Saturn's rings

The last phases of the Cassini mission have as a primary target the determination of the asymmetry of the internal dynamo-generated field of Saturn. Standard methods for data inversion require the data to be from a region devoid of currents. What this implies will be discussed and, in particular the evidence for electromagnetic effects in the immediate ring environment will be discussed by re-examining the data from the insertion orbit of Cassini when the spacecraft flew as close as 1.33RS radial distance.

2. Is the Saturn magnetosphere good model of a pulsar?

The simplest (and widely accepted) model of a pulsar is that radio signals are emitted from the magnetosphere of a collapsed neutron star in which rotation and magnetic axes are aligned. A simple symmetry argument shows that such a system should not actually pulse. Saturn is an aligned rotator; could this resolve a more than 40 yr old enigma? (Ans: Yes)

3. Alfvén waves and MHD instability/reconnection

Alfvén waves, the intermediate mode of MHD, are critical in communicating field aligned currents, and thus stress between the planetary ionosphere and magnetosphere. MHD instability (due plasma anisotropy or inhomogeneity, including most macroscopic models of reconnection) occurs usually in conditions where the intermediate propagation speed is zero (or imaginary). The implications of this for Saturn's magnetosphere are fairly clear but in the terrestrial context (where emotional arguments on substorms hinge on timing) the issue is rarely raised. Should it be?