HR: 1400h
AN: SM23C-03    [Abstracts]
TI: Role of Reconnection and Ballooning Modes in the Near-Earth Neutral Line Model
AU: Zhu, P
EM: pzhu@wisc.edu
AF: Center for Plasma Theory and Computation, University of Wisconsin, Madison, WI 53706, United States
AU: * Bhattacharjee, A
EM: amitava.bhattacharjee@unh.edu
AF: Space Science Center, University of New Hampshire, Durham, NH 03824, United States
AU: Germascheski, K
EM: kai.germaschewski@unh.edu
AF: Space Science Center, University of New Hampshire, Durham, NH 03824, United States
AU: Hegna, C
EM: hegna@cae.wisc.edu
AF: Space Science Center, University of New Hampshire, Durham, NH 03824, United States
AU: Sovinec, C
EM: sovinec@engr.wisc.edu
AF: Center for Plasma Theory and Computation, University of Wisconsin, Madison, WI 53706, United States
AB: Recent developments in the theory of collisionless reconnection and nonlinear ballooning instabilities in the Earth's magnetotail, tested by observations from Wind and Cluster, have brought new insights to bear on the classical Near-Earth Neutral Line model. These developments underscore the importance of collisionless reconnection in producing an X-line at mid-tail distances (~30 Re) and the growth of a thin and intense current sheet that mediates the development of very strong pressure gradients at near-Earth distances (~10 Re). In turn, these pressure gradients excite ballooning instabilities that are manifested as a westward traveling surge, which can be inferred by analyzing the time-delay between earthward and tailward flux enhancements of energetic ions. The eneregtic ion data also suggests a strong pre-onset pressure gradient that is reduced impulsively at onset. New developments in the theory and simulation of nonlinear ballooning modes appear to be consistent with these observations. Furthermore, the theory predicts the generation of finger-like structures and strongly sheared flows as a consequence of the instability, which pose new challenges for observations. However, despite the robust nonlinear growth of ballooning modes at near-Earth distances, it cannot be claimed that ballooning modes, by themselves, can account for all the important signatures of substorm onset. We will discuss open questions, and directions in which theoretical and modeling studies need to be extended in order to obtain a more complete theory of substorm onset.
DE: 2723 Magnetic reconnection (7526, 7835)
DE: 2744 Magnetotail
DE: 2752 MHD waves and instabilities (2149, 6050, 7836)
DE: 2753 Numerical modeling
DE: 2790 Substorms
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Joint Assembly