Paper#: 150
Poster #:
Session Name: Workshop 2B: Particle/MHD Substorms
Room: 200ABC
Day: Monday
Time: 2:15-2:40 p.m.
Abstract Title: Role of Collisionless Reconnection and Ballooning Instabilities in Substorm Dynamics
PresentSurname: Bhattacharjee, A.
All Authors: A. Bhattacharjee, L.-J. Chen, Z.W. Ma
Abstract : We present a theory of substorm dynamics within the framework of the Hall magnetohydrodynamics (MHD) model, using analysis as well as high-resolution numerical simulations. The Hall MHD model, which uses multi-fluid equations, is an interesting compromise between resistive MHD and fully kinetic particle-in-cell models because it includes important kinetic effects but does so within the framework of a fluid model. Our studies clarify the role of collisionless reconnection and ballooning instabilities in the different dynamical phases of a magnetotail substorm. It is shown that collisionless reconnection plays an important role in the growth phase of a substorm by facilitating the growth of extended Y-type thin current sheets that are initiated at mid-tail distances ( approximately 30 RE) and stretch inward. Due to Hall MHD effects, the thin current sheet exhibits an impulsive pre-onset enhancement at near-Earth distances (approximately 10 RE) on a rapid time scale that is very weakly dependent on the plasma resistivity. Although magnetic reconnection plays an important role in the growth and pre-onset phase of a substorm, it does not appear to account for significant features of substorm onset. We propose instead that a Hall MHD ballooning instability, with rapid variation along y, provides a possible mechanism for disrupting the cross-tail current at substorm onset. The results of our analysis and Hall MHD simulations are compared with WIND and ground-based observations.