ESC seminar No. 47
Mechanism for reversals
- Date
- Dec. 17 (Wed.), 2008, 15:00-16:00
- Place
- Seminar Room. 1F, Earth Simulator Research Building, YES, JAMSTEC
- Speaker
- Dr. Francois Petrelis (Ecole Normale Superieure (France))
- Language
- English
Abstract
Geophysical and astrophysical observations and recent experimental measurements have shown that the magnetic field generated by dynamo instability can display complex dynamics such as random or periodic reversals.
We show that these behaviours result from the competition between two nearly critical modes of magnetic field. The basic ingredient is that the two modes are close to achieve a saddle-node bifurcation and to generate a finite amplitude limit cycle. In the vicinity of this bifurcation, even a small amount of turbulent fluctuations is sufficient to initiate random reversals of the magnetic field.
Based on this scenario, predictions can be made about the shape and the statistics of the reversals. The mechanism also predicts the existence of aborted reversals (excursions) and of long durations with no reversals (superchrons). These predictions are compared with the measurements of the Earth magnetic field and of an experiment that studies a turbulent swirling flow of liquid sodium (the Von Karman Sodium experiment).
Contact
Takehiro MiyagoshiSolid Earth Simulation Research Group
Computational Earth Science Research Program
Earth Simulator Center TEL: 045-778-5839
e-mail:
