Paper#: 81
Poster #:
Session Name: Workshop 6A: Ionospheric Process
Room: 200ABC
Day: Thursday
Time: 1:55-2:15 p.m.
Abstract Title: Onset of Substorm Triggered by Field-Aligned Current at Electrons' Field-Aligned Traveling Time Scale
PresentSurname: Lyu, L.H.
All Authors: L.H. Lyu
Abstract : It is shown in this study that onset of substorm can be triggered by a field-aligned current carried primarily by electrons on their way back into ionosphere. Due to non-uniform distribution of partial ring current, the diffuse aurora is expected to have maximum poleward gradient in the pre-midnight region. Quiet aurora arc during growth phase can further enhance gradient of ionospheric conductivities. The gradient of anisotropic conductivities in the E-region can lead to non-uniform rotation of electric field and result in a left-hand rotated E-field vortex in this region. ExB drift can suck electrons into center of the vortex to produce a cluster of electrons. Before ions can response to the perpendicular gradient of charge density, these electrons are accelerated by the field-aligned E-field and move upward into higher latitude. An electrostatic simulation is carried out to study field-aligned electron acceleration in this region. It is shown that due to large potential differences at the center of the vortex, a downward field-aligned current can quickly expend into the near-Earth plasma sheet. As these electrons coming back into ionosphere, an upward field-aligned current is generated. Magnetic field configuration changes due to presence of these field-aligned currents are evaluated separately. Our results indicate that the initial upward motion of electron beams can lead to explosive thinning of near-Earth plasma sheet, whereas, the returning electron beams can trigger dipolarization at a time scale of electrons' field-aligned traveling time, which is much shorter than the traveling time of an Alfven wave.