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| Titel |
Turbulent fluctuations at kinetic scales: from coherent structures to quasi-parallel whistler waves |
| VerfasserIn |
Olga Alexandrova, Catherine Lacombe, Lorenzo Matteini, Claudia Rossi, Milan Maksimovic, André Mangeney, Ondrej Santolik, Nicole Cornilleau-Wehrlin, Yvonne de Conchy |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250112476
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| Publikation (Nr.) |
 EGU/EGU2015-12636.pdf |
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| Zusammenfassung |
| The nature of the magnetic field fluctuations in the solar wind between the ion and electron
scales is still under debate. Using the Cluster/STAFF instrument, we make a survey of the
power spectral density and of the polarization of these fluctuations at frequencies
f / [1,400]ÂHz, during five years (2001–2005) when Cluster was in the free solar wind. In
most of the analyzed time intervals, the fluctuations have quasi-random polarization and they
have a general spectral shape between the ion scales and a fraction of electron scales. The
intensity of these spectra is well correlated to the ion thermal pressure. These fluctuations
seem to have a negligible frequency in the solar wind frame, and a wavevector
anisotropy k/¥ ≈« k/¥. Such time intervals are dominated by coherent structures,
propagating with a finit velocity in the plasma frame, in the plane perpendicular
to the mean magnetic field. In the rest ~ 10% of the selected data, we observe
narrow-band, right-handed, circularly polarized fluctuations, with wave vectors
quasi-parallel to the mean magnetic field, superimposed on the spectrum of the
permanent background turbulence. We interpret these coherent fluctuations as whistler
mode waves. The life time of such waves varies between a few seconds and several
hours. We analyze in details the long-lived whistler waves, i.e. with a life time
longer than five minutes. When the electron parallel beta factor βe/¥ is larger than 3,
the whistler waves are seen along the heat flux threshold of the whistler heat flux
instability. |
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