Substorm triggering by new plasma intrusion: THEMIS all-sky imager observations

被引:217
作者
Nishimura, Y. [1 ,2 ]
Lyons, L. [1 ]
Zou, S. [1 ,3 ]
Angelopoulos, V. [4 ]
Mende, S. [5 ]
机构
[1] Univ Calif Los Angeles, Dept Atmospher & Ocean Sci, Los Angeles, CA 90095 USA
[2] Nagoya Univ, Solar Terr Environm Lab, Nagoya, Aichi 4648601, Japan
[3] Univ Michigan, Dept Atmospher Ocean & Space Sci, Ann Arbor, MI 48109 USA
[4] Univ Calif Los Angeles, Inst Geophys & Planetary Phys, Los Angeles, CA 90095 USA
[5] Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA
基金
美国国家科学基金会;
关键词
POLEWARD BOUNDARY INTENSIFICATIONS; MAGNETOSPHERIC SUBSTORMS; AURORAL STREAMERS; ONSET; ASSOCIATION; MIDNIGHT; SHEET;
D O I
10.1029/2009JA015166
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
A critical, long-standing problem in substorm research is identification of the sequence of events leading to substorm auroral onset. Based on event and statistical analysis of THEMIS all-sky imager data, we show that there is a distinct and repeatable sequence of events leading to onset, the sequence having similarities to and important differences from previous ideas. The sequence is initiated by a poleward boundary intensification (PBI) and followed by a north-south (N-S) arc moving equatorward toward the onset latitude. Because of the linkage of fast magnetotail flows to PBIs and to N-S auroras, the results indicate that onset is preceded by enhanced earthward plasma flows associated with enhanced reconnection near the pre-existing open-closed field line boundary. The flows carry new plasma from the open field line region to the plasma sheet. The auroral observations indicate that Earthward-transport of the new plasma leads to a near-Earth instability and auroral breakup similar to 5.5 min after PBI formation. Our observations also indicate the importance of region 2 magnetosphere-ionosphere electrodynamic coupling, which may play an important role in the motion of pre-onset auroral forms and determining the local times of onsets. Furthermore, we find motion of the pre-onset auroral forms around the Harang reversal and along the growth phase arc, reflecting a well-developed region 2 current system within the duskside convection cell, and also a high probability of diffuse-appearing aurora occurrence near the onset latitude, indicating high plasma pressure along these inner plasma sheet field lines, which would drive large region 2 currents.
引用
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页数:14
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