Other
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsm52b..03j&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #SM52B-03
Other
2740 Magnetospheric Configuration And Dynamics, 2744 Magnetotail, 2752 Mhd Waves And Instabilities, 2764 Plasma Sheet
Scientific paper
The plasma distribution function observed in a Bursty Bulk Flow (BBF) often exhibits one beam flowing through another, which raises the question of whether BBFs can reasonably be represented in terms of single-fluid magnetohydrodynamics, either in global MHD codes or in the thin-filament theory. Study of a simplified case suggests that double-adiabatic MHD is more realistic than ordinary MHD for situations with counter-streaming beams. Motivated by this result, we derive double-adiabatic MHD equations describing the motion of a thin filament through a medium. The dispersion relationships for linear waves are the same as in anisotropic MHD in an infinite homogenous medium and thus exhibit firehose and mirror instabilities, for transverse and longitudinal waves, respectively. We have developed a double-adiabatic MHD code to represent the motion of a thin filament moving through Earth's plasma sheet. An initial simulation shows the evolution of a double-adiabatic filament that starts out with lower gas pressure than nearby flux tubes. The near-equatorial part of the filament moves rapidly earthward, and a compressional shock wave propagates earthward along the filament. The near-equatorial region of the filament exhibits characteristics similar to a flow burst, while the behavior far from the equatorial plane resembles that of earthward-streaming plasma-sheet boundary layer. After the shock reflects from the earthward boundary of the simulation, the filament resembles a two-beam plasma-sheet boundary layer. The double-adiabatic filament tends to be firehose unstable, particularly after the shock wave reflects from the earthward boundary of the simulation.
Ji Shaolin
Wolf Richard A.
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