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| Titel |
Variability of the magnetic field power spectrum in the solar wind at electron scales |
| VerfasserIn |
Owen Roberts, Primoz Kajdic, Olga Alexandrova, Lucile Turc, Philippe Escoubet, Andrew Walsh |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250148846
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| Publikation (Nr.) |
 EGU/EGU2017-13139.pdf |
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| Zusammenfassung |
| Solar wind magnetic fluctuations show the presence of several power laws. At the electron
scales the power spectrum can be highly variable and the dissipation mechanisms of the
magnetic field energy into the various particle species remain under debate. In this paper we
investigate the morphology of the power spectrum at electron scales using data from
the Cluster mission’s Search coil magnetometer when the Cluster spacings were
∼ 10000km. By using wavelet coherence on the magnetic field data, times when the
magnetic field signals are characteristic of certain phenomena such as whistler waves
and coherent structures can be identified. Several different morphologies of the
power spectrum are seen including: (1) two power laws separated by a break (2) an
exponential cutoff near the Taylor shifted electron scales (3) strong spectral knees at the
Taylor shifted electron scales .The different morphologies of the power spectrum are
investigated by using wavelet coherence and show that in this interval a clear break
and strong spectral knees are features which are associated with sporadic quasi
parallel propagating whistler waves. Meanwhile when no signatures of whistler
waves are present a clear break is difficult to find and the spectrum is often more
characteristic of a power law with an exponential cutoff . The presence of these waves
even for short times in an interval can affect the spectral shape drastically, and
cause pitch angle scattering of electrons. The electron temperature and the electron
heat flux measurements do not show unstable conditions to generate whistlers.,
however in several cases they are seen to be related to discontinuities in the large scale
magnetic field. While large scale discontinuities are often seen at all spacecraft, not
all spacecraft are accompanied with whistler waves which we interpret as being
related to the geometry of the discontinuity and the path of the spacecraft through the
plasma. It is possible that in the vicinity of these discontinuities, electron distribution
functions are distorted and so unstable, but we cannot capture these distortions because
of insufficient time, energy and angular resolution of the particle measurements. |
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