HR: 0800h
AN: SM31B-1239    [Abstracts]
TI: Firehose Turbulence as the Source of Pi2 Precursors to Dipolarization Events
AU: * Horton, W
EM: horton@physics.utexas.edu
AF: The University of Texas at Austin, Institute for Fusion Studies RLM 11.320, Austin, TX 78712 United States
AU: Wong, V
EM: navajo@mail.utexas.edu
AF: The University of Texas at Austin, Institute for Fusion Studies RLM 11.320, Austin, TX 78712 United States
AB: The nonlinear dynamics of the firehose instability provides a possible explanation for the onset of the magnetic fluctuations associated with bursty bulk flows and substorms. The Pi2 geomagnetic pulsations are observed as precursors to the dipolarization events associated with substorms and sawtooth injections [Kepko and Kivelson, JGR 2001 and Sigsbee et al., JGR 2002]. A scenario of rapid Earthward flux tube motion producing a parallel ion pressure anisotropy triggering firehose driven Alfven wave turbulence is presented. Kinetically corrected MHD theory is required to describe the nonlinear magnetic fluctuations. Strong magnetic fluctuations are typically associated with substorms and start a few minutes before the arrival of the dipolarization pulse. Secondary current driven instabilities are considered and may also be seen in the data at ion cyclotron and lower hybrid frequencies. Nonlinear saturation is caused by the nonlinear weakening at large magnetic field line distortions of the destabilizing magnetic curvature force driven by the pressure anisotropy. Horton, W., B.-Y. Xu, and H. Vernon Wong, Firehose driven magnetic fluctuations in the magnetosphere, GRL 31, 2004. This work was supported by National Science Foundation Grant ATM-0229863.
DE: 2730 Magnetosphere--inner
DE: 2740 Magnetospheric configuration and dynamics
DE: 2760 Plasma convection
DE: 2772 Plasma waves and instabilities
DE: 2788 Storms and substorms
SC: SPA-Magnetospheric Physics [SM]
MN: 2004 AGU Fall Meeting