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Title: Substorm simulation: Formation of westward traveling surge
Authors: Ebihara, Y.
Tanaka, T.
Author's alias: 海老原, 祐輔
田中, 高史
Keywords: Substorm
Westward traveling surge
Aurora
Field-aligned current
Magnetosphere-ionosphere coupling
Simulation
Issue Date: 21-Dec-2015
Publisher: American Geophysical Union
Journal title: Journal of Geophysical Research: Space Physics
Volume: 120
Issue: 12
Start page: 10466
End page: 10484
Abstract: Auroral substorm expansion is characterized by initial brightening of aurora, followed by a bulge expanding in all directions, and a westward traveling surge (WTS). On the basis of the result obtained by a global magnetohydrodynamic (MHD) simulation, we propose a scenario for the onset and the subsequent formation of WTS. (1) Near-Earth neutral line releases magnetic tension in the near-Earth plasma sheet to compress plasma and accelerate it earthward. (2) Earthward, perpendicular flow is converted to parallel flow when flow braking takes place. (3) Plasma moves earthward parallel to a field line. The plasma pressure is additionally enhanced at off-equator with an expanding slow mode variation. (4) Flow vorticities coexist near the off-equatorial high-pressure region. Resultant field-aligned current (FAC) is connected to the ionosphere, which may manifest initial brightening. (5) Due to continued earthward flow, the high-plasma pressure region continues to expand to the east and west. (6) The ionospheric conductivity continues to increase in the upward FAC region, and the conductivity gradient becomes steeper. (7) The convergence of the Hall current gives rise to divergent electric field near the steep gradient of the conductivity. (8) Due to the divergent electric field, magnetospheric plasma moves counterclockwise at low altitude (in the Northern Hemisphere). (9) The additional flow vorticity generates a localized upward FAC at low altitudes, which may manifest WTS, and redistribute the ionospheric current and conductivity. Thus, WTS may be maintained in a self-consistent manner, and be a natural consequence of the overflow of the Hall current.
Description: オーロラ爆発はなぜ起こるのか? --スーパーコンピューターでオーロラ爆発の基本的な仕組みを明らかに--. 京都大学プレスリリース. 2015-12-21.
Rights: ©2015 American Geophysical Union.
The full-text file will be made open to the public on 21 June 2016 in accordance with publisher's 'Terms and Conditions for Self-Archiving'.
URI: http://hdl.handle.net/2433/202825
DOI(Published Version): 10.1002/2015JA021697
Related Link: http://www.kyoto-u.ac.jp/ja/research/research_results/2015/151221_1.html
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