A current disruption mechanism in the neutral sheet - A possible trigger for substorm expansions

Details A current disruption mechanism in the neutral sheet - A possible trigger for substorm expansions A current disruption mechanism in the neutral sheet - A possible trigger for substorm expansions

May 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990georl..17..745l&link_type=abstract

Geophysical Research Letters (ISSN 0094-8276), vol. 17, May 1990, p. 745-748.

Physics

92

Geomagnetic Tail, Magnetic Storms, Magnetohydrodynamic Stability, Neutral Sheets, Space Plasmas, Crossed Fields, Electric Fields, Wave Excitation, Whistlers

Scientific paper

A linear analysis is performed to investigate the kinetic cross-field streaming instability in the earth's magnetotail neutral sheet region. Numerical solution of the dispersion equation shows that the instability can occur under conditions expected for the neutral sheet just prior to the onset of substorm expansion. The excited waves are obliquely propagating whistlers with a mixed polarization in the lower hybrid frequency range. The ensuing turbulence of this instability can lead to a local reduction of the cross-tail current causing it to continue through the ionosphere to form a substorm current wedge. A substorm expansion onset scenario is proposed based on this instability in which the relative drift between ions and electrons is primarily due to unmagnetized ions undergoing current sheet acceleration in the presence of a cross-tail electric field. The required electric field strength is within the range of electric field values detected in the neutral sheet region during substorm intervals. The skew in local time of substorm onset location and the three conditions under which substorm onset is observed can be understood on the basis of the proposed scenario.

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