ANGEO Annales Geophysicae ANGEO 1432-0576 Copernicus GmbH Göttingen, Germany 10.5194/angeo-27-1941-2009 Disruption of magnetospheric current sheet by quasi-electrostatic field Liu W. W. 1 Liang J. 1 Space Science Branch, Canadian Space Agency, Canada 04 05 2009 27 5 1941 1950 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.ann-geophys.net/27/1941/2009/angeo-27-1941-2009.html The full text article is available as a PDF file from http://www.ann-geophys.net/27/1941/2009/angeo-27-1941-2009.pdf

Recent observational evidence has indicated that local current sheet disruptions are excited by an external perturbation likely associated with the kinetic ballooning (KB) instability initiating at the transition region separating the dipole- and tail-like geometries. Specifically a quasi-electrostatic field pointing to the neutral sheet was identified in the interval between the arrival of KB perturbation and local current disruption. How can such a field drive the local current sheet unstable? This question is considered through a fluid treatment of thin current sheet (TCS) where the generalized Ohm's law replaces the frozen-in-flux condition. A perturbation with the wavevector along the current is applied, and eigenmodes with frequency much below the ion gyrofrequency are sought. We show that the second-order derivative of ion drift velocity along the thickness of the current sheet is a critical stability parameter. In an E-field-free Harris sheet in which the drift velocity is constant, the current sheet is stable against this particular mode. As the electrostatic field grows, however, potential for instability arises. The threshold of instability is identified through an approximate analysis of the theory. For a nominal current sheet half-thickness of 1000 km, the estimated instability threshold is <I>E</I>~4 mV/m. Numerical solutions indicate that the two-fluid theory gives growth rate and wave period consistent with observations.

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