Physics
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsm14a..08p&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #SM14A-08
Physics
7839 Nonlinear Phenomena, 7843 Numerical Simulation Studies, 2744 Magnetotail, 2764 Plasma Sheet
Scientific paper
In the near-Earth plasma sheet the pressure gradient and magnetic curvature are both directed earthward. This region is thus potentially unstable to the pressure-gradient ballooning mode provided that the plasma β becomes large enough. Theoretical analysis of the critical β for this mode has been inconclusive: the applicability of MHD (which gives a low critical β ) to the near-Earth tail current sheet just prior to substorm onset is dubious, and kinetic analyses, which are exceedingly complex, have reached contradictory conclusions. Early particle-in-cell (PIC) simulations with a very low mass ratio mi/m_e = 16 suggested that an alternative interchange mode, the high-β mode, may indeed be more robust than the standard pressure gradient mode. The signature of this mode is that it occurs in regions of a tailward-directed gradient in the equatorial magnetic field; the mode is driven by the need to return magnetic flux to the dipole region. A massively-parallel 3D PIC code is used to study the properties of the high-β mode for more realistic values of mi/m_e ˜ 100. The initial configuration consists of a 2D generalized Harris current sheet with a minimum Bz region. The simulations are used to determine the minimal conditions required to excite the instability, to map out the unstable mode spectrum in ky, and to establish the nonlinear properties of the magnetic field and plasma configurations.
Coroniti Ferdinan V.
Pritchett Philip L.
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