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Evidence of kinetic Alfvén eigenmode in the near-Earth magnetotail during substorm expansion phase
- Source :
- Journal of Geophysical Research: Space Physics. 121:4316-4330
- Publication Year :
- 2016
- Publisher :
- American Geophysical Union (AGU), 2016.
-
Abstract
- Unipolar pulses of kinetic Alfven waves (KAW) are first observed in the near-Earth plasma sheet (NEPS) associated with dipolarizations during substorm expansion phases. Two similar events are studied with Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations during substorms on 3 February 2008 and 7 February 2008. The unipolar pulses were located at a trough-like Alfven speed profile in the northern plasma sheet at a distance of 10–11 R E from Earth. The dominant wave components consist of a southward δ E z toward the neutral plane and a +δ B y toward the dusk. The |δ E z |/|δ B y | ratio was in the range of a few times the local Alfven speed, a strong indication of KAW nature. The wave Poynting flux was earthward and nearly parallel to the background magnetic field. The pulse was associated with an earthward field-aligned current carried by electrons. These observational facts strongly indicate a KAW eigenmode that is confined by the plasma sheet but propagates earthward along the field line. The KAW eigenmode was accompanied by short timescale (1 min) dipolarizations likely generated by transient magnetotail reconnection. The observed polarity of the KAW field/current is consistent with that of the Hall field/current in magnetic reconnection, supporting the scenario that the Hall fields/current propagate out from reconnection site as KAW eigenmodes. Aurora images on the footprint of THEMIS spacecraft suggest that KAW eigenmode may power aurora brightening during substorm expansion phase.
- Subjects :
- Physics
010504 meteorology & atmospheric sciences
Field (physics)
Field line
Plasma sheet
Flux
Magnetic reconnection
Geophysics
01 natural sciences
Computational physics
Magnetic field
Space and Planetary Science
0103 physical sciences
Substorm
Poynting vector
010306 general physics
0105 earth and related environmental sciences
Subjects
Details
- ISSN :
- 21699380
- Volume :
- 121
- Database :
- OpenAIRE
- Journal :
- Journal of Geophysical Research: Space Physics
- Accession number :
- edsair.doi...........12267121da9912aff9c4eddd0798d7ed