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Titel |
Solar wind turbulent cascade between ion and electron scales and quasi-parallel whistler waves |
VerfasserIn |
Olga Alexandrova, Catherine Lacombe, André Mangeney, Roland Grappin, Milan Maksimovic |
Konferenz |
EGU General Assembly 2014
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 16 (2014) |
Datensatznummer |
250093460
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Publikation (Nr.) |
EGU/EGU2014-8192.pdf |
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Zusammenfassung |
The solar wind is probably the best laboratory to study turbulence in astrophysical plasmas.
In addition to the presence of a magnetic field, the differences with neutral fluid isotropic
turbulence are: (i) weakness of collisional dissipation and (ii) presence of several
characteristic space and time scales. Here we focus on the observational properties of the
solar wind magnetic field turbulence around ion and electron characteristic scales. Around
ion scales, magnetic spectra are variable and ion instabilities occur as a function of the
local plasma parameters. Between ion and electron scales, a small scale turbulent
cascade seems to be established, with wave vectors k-¥ mainly perpendicular to
the average B field. It is characterised by a well defined power-law spectrum in
magnetic and density fluctuations with a spectral index close to -2.8. Approaching
electron scales, the fluctuations are no more self-similar: an exponential cut-off is
usually observed indicating an onset of dissipation. The small scale inertial range
between ion and electron scales and the electron dissipation range can be together
described by ~ k-¥-α exp(-k-¥-d), with α -ă 8-3 and the dissipation scale -d close to
the electron Larmor radius -d -ă Ïe. The nature of this small scale cascade and a
possible dissipation mechanism are still under debate. Different spectra are however
observed in some regions of the solar wind, with quasi-parallel whistlers between
the lower hybrid frequency and about half the electron cyclotron frequency. Such
whistler waves may have variable intensity with respect to the background turbulence.
Consequently, the total magnetic spectra may present a break, a knee or a more or
less intense bump around frequencies at which whistlers propagate. We discuss a
possible generation mechanism of quasi-parallel whistler waves in the solar wind. |
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