Physics
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsm31d0659j&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SM31D-0659
Physics
2723 Magnetic Reconnection (7526, 7835), 2744 Magnetotail, 2764 Plasma Sheet
Scientific paper
Recent simulations of collisionless reconnection and spacecraft observations in the magnetotail and magnetopause have shown the existence of very thin electron current sheets, with scale lengths of the order of a few electron skin depths. The stability of such current sheets is crucial to the understanding of the onset of reconnection. A two-dimensional electron-magnetohydrodynamic (EMHD) model is used to simulate the dynamics on such short space and time scales. The simulations of a thin electron current sheet with anti-parallel magnetic field show the development of whistler-like perturbations, leading to magnetic reconnection. In the EMHD model, reconnection of field lines is facilitated by electron inertia which provides the non-ideal effect in Ohm's law and breaks the frozen-in condition. The whistler mode structure and growth rate are obtained from the numerical solutions of the eigen-mode equations derived from the linearized EMHD model. These agree well with the full simulations, confirming the instability of the whistler-like mode. The linear eigen-mode analysis shows that modes with wavelengths smaller than the equilibrium scale length are stable, while those of the order of or greater than the equilibrium scale length are unstable. The growth rate reduces monotonically with the ratio of equilibrium scale length and electron skin depth, indicating that the instability is driven by finite electron inertia. The simulation shows that the instability initiates the reconnection of the field lines, with the reconnection rate determined by the growth rate of the instability. As the reconnection progresses the out of plane magnetic field develops a quadrupole structure over the reconnection region. The reconnection slows down with the saturation of the instability, and the initial single peak of the electron current sheet develops multiple peaks and its magnitude is reduced, yielding a bifurcated current sheet. Three-dimensional studies are in progress and will be compared with these results.
Jain Nitin
Sharma Surjalal A.
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