A note on the interchange stability criterion
Abstract
The correct stability criterion of interchange motions in the magnetosphere has been a question of some controversy. Many researchers hold the view first espoused by Gold [1959]. For a low-β plasma in a dipole magnetic field, Gold argued that the gradient of pVγ, where p is the plasma pressure, V is the unit flux tube volume, and γ is the adiabatic polytropic index, determines the interchange stability. This notion was further developed by Chandrasekhar [1960]. This common belief was questioned by Cheng [1985], who was subsequently questioned by Rogers and Sonnerup [1986] and Southwood and Kivelson [1987] on the issue. Is Gold's criterion the necessary and sufficient condition for interchange stability? We shall demonstrate that the answer is ``no'' and provide a more accurate criterion for the dipole magnetic field. We shall also discuss the interchange instability in a plasma distribution with a longitudinal gradient.
- Publication:
-
Journal of Geophysical Research
- Pub Date:
- December 1996
- DOI:
- 10.1029/96JA02787
- Bibcode:
- 1996JGR...10127443L
- Keywords:
-
- Magnetospheric Physics: Magnetospheric configuration and dynamics;
- Magnetospheric Physics: MHD waves and instabilities;
- Space Plasma Physics: Charged particle motion and acceleration;
- Space Plasma Physics: Kinetic and MHD theory