This thesis is a theoretical study about the Earth's tail plasma sheet with regard to two aspects: the equilibrium structure for the anisotropic pressure, and the ideal-MHD ballooning stability. By adopting a stretched magnetotail model where ion motions are generally nonadiabatic, and assuming that the anisotropy resides only in the electron pressure tensor, it is shown that the magnetic field lines with $\rm p\sb\perp > p\sb\Vert$ are less stretched than the isotropic cases. As the parallel pressure p$\sb\Vert$ exceeds the perpendicular pressure p$\sb\perp$ approaching the conventional marginal firehose limit, $\rm p\sb\Vert = p{\sb\perp}$ + B$\sp2$/$\mu\sb0$, the magnetic field lines are more and more stretched. It is also shown that the current density is highly enhanced at the same limit, a situation that might be subject to a microscopic instability. However, we also emphasize that such an enhancement in the current density is heavily localized near the z = 0 plane, and thus it is unclear if such a microscopic instability can significantly alter the global configuration of the tail. It is further argued, in terms of the radius of the field curvature versus the particle's gyroradius, that the conventional adiabatic description of electrons may become questionable, very close to the conventional marginal firehose limit.
To study the ideal-MHD ballooning mode, we first adopt a hard ionospheric boundary condition where the perturbation is required to vanish at the ionospheric foot points. For such a hard boundary condition, an "untypical" magnetic field configuration is found to be unstable to a ballooning mode that is antisymmetric about the equatorial plane while most of the "typical" tail plasma-sheet configurations are stable against the ideal-MHD ballooning mode. The unstable magnetic field model, however, does not look like the average observation-based model, but rather resembles some of the characteristics of the steady-state magnetic field models by Hau (1989, 1991). In addition, a physical argument is presented to show that the hard ionospheric boundary condition is the most appropriate simple boundary condition for the Earth's plasma sheet.
| Identifer | oai:union.ndltd.org:RICE/oai:scholarship.rice.edu:1911/16641 |
| Date | January 1993 |
| Creators | Lee, Dae-Young |
| Contributors | Voigt, G.-H. |
| Source Sets | Rice University |
| Language | English |
| Detected Language | English |
| Type | Thesis, Text |
| Format | 115 p., application/pdf |
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