Physics of Substorm Growth Phase and Onset

Details Physics of Substorm Growth Phase and Onset Physics of Substorm Growth Phase and Onset

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsm23b0419c&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #SM23B-0419

Physics

2764 Plasma Sheet, 2790 Substorms, 7827 Kinetic And Mhd Theory

Scientific paper

Space and ground-based observations have indicated that the substorm onset in the near-Earth plasma sheet region (~ 8-10 R_E) is associated with a low frequency (in the Pi 2 range) instability. The instability has been explained as kinetic ballooning modes (KBMs) which are excited when βeq increases from ~ 20 to above 50. The global magnetosphere prior to substorm onset is modeled realistically by 3D quasi-static equilibrium solutions which consist of a current sheet with an enhanced cross-tail current density with thickness of ~ 1 R_E around the local midnight and with a longitudinal extent of ~ 60-70° at X ~ - (7-11) R_E. The associated ionospheric Birkeland current moves equatorward with an enhanced current density shrinking in latitudinal width, consistent with the observed ionospheric growth phase signatures. To study the onset instability, we present theoretical analysis and numerical solutions of KBMs, which include kinetic effects of particle trapping, finite ion gyroradii, and wave-particle resonances. The results indicate that a new branch of unstable KBM is destabilized through wave-ion magnetic drift resonance. The KBM has a real frequency in the Pi2 frequency range. The kinetic calculations will be compared with the MHD theory.

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