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| Titel |
A mechanism for heating electrons in the magnetopause current layer and adjacent regions |
| VerfasserIn |
A. Roux, P. Robert, O. Contel, V. Angelopoulos, U. Auster, J. Bonnell, C. M. Cully, R. E. Ergun, J. P. McFadden |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 29, no. 12 ; Nr. 29, no. 12 (2011-12-23), S.2305-2316 |
| Datensatznummer |
250017147
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| Publikation (Nr.) |
 copernicus.org/angeo-29-2305-2011.pdf |
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| Zusammenfassung |
| Taking advantage of the string-of-pearls configuration of the five THEMIS
spacecraft during the early phase of their mission, we analyze observations
taken simultaneously in the magnetosheath, the magnetopause current layer and
the magnetosphere. We find that electron heating coincides with ultra low
frequency waves. It seems unlikely that electrons are heated by these waves
because the electron thermal velocity is much larger than the Alfvén
velocity (Va). In the short transverse scale (k⊥ρi >> 1)
regime, however, short scale Alfvén waves (SSAWs) have parallel phase
velocities much larger than Va and are shown to interact, via Landau
damping, with electrons thereby heating them. The origin of these waves is
also addressed. THEMIS data give evidence for sharp spatial gradients in the
magnetopause current layer where the highest amplitude waves have a large
component δB perpendicular to the magnetopause and k azimuthal. We
suggest that SSAWs are drift waves generated by temperature gradients in a
high beta, large Ti/Te magnetopause current layer. Therefore these waves
are called SSDAWs, where D stands for drift. SSDAWs have large k⊥ and
therefore a large Doppler shift that can exceed their frequencies in the
plasma frame. Because they have a small but finite parallel electric field
and a magnetic component perpendicular to the magnetopause, they could play a
key role at reconnecting magnetic field lines. The growth rate depends
strongly on the scale of the gradients; it becomes very large when the scale
of the electron temperature gradient gets below 400 km. Therefore SSDAW's are
expected to limit the sharpness of the gradients, which might explain why
Berchem and Russell (1982) found that the average magnetopause current sheet
thickness to be ~400–1000 km (~500 km in the near equatorial
region). |
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