Quasi-separatrix Layers Induced by Ballooning Instability in Near-Earth Magnetotail*

Abstract:

Recent MHD simulations indicate that the magnetic reconnection processes in the near-Earth magnetotail can be highly 3-dimensional in geometry and dynamics, even though the magnetotail configuration itself is nearly two dimensional due to the symmetry in the dusk-dawn direction. These reconnection processes are in fact induced by the intrinsically 3D process of nonlinear ballooning instability [1,2]. Where and how 3D reconnection occurs is crucial for determining its consequences in both the magnetotail and the auroral regions. In this work, we focus on examining the geometric aspects of the 3D reconnection process induced by ballooning instability in the near-Earth magnetotail by computing the bald patches and squashing degrees of the magnetic field lines associated with the 3D plasmoid formation. The periodic distributions of both bald patches and quasi-separatrix layers (QSL) correlate closely with the ballooning finger pattern, revealing the intrinsically 3D nature of the coupling between the reconnection process and the ballooning instability. Despite the 3D geometry involved, the QSL pattern in the equatorial plane as well as its mapping in the auroral region is 2-dimensional. This may provide an alternative means for identifying the magnetotail origins of the auroral structures during substorm process.

*Research supported by U.S. NSF grant AGS-0902360 and USTC 100-Talent program.

[1] P. Zhu and J. Raeder, Plasmoid formation in current sheet with finite normal magnetic component, Phys. Rev. Lett. 110, 235005 (2013).

[2] P. Zhu and J. Raeder, Ballooning instability-induced plasmoid formation in near-Earth plasma sheet, J. Geophys. Res. Space Physics 119, 131-141 (2014).