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| Titel |
ULF waves and plasma stability in different regions of the magnetosheath |
| VerfasserIn |
Jan Soucek, C. Philippe Escoubet, Benjamin Grison |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250126957
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| Publikation (Nr.) |
 EGU/EGU2016-6753.pdf |
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| Zusammenfassung |
| We present a statistical study of the occurrence and properties of ultra low frequency waves in
the magnetosheath and interpret the results in terms of the competition of mirror and
Alfvén-ion-cyclotron (AIC) instabilities. Both mirror and AIC waves are generated in high
beta plasma of the magnetosheath when ion temperature anisotropy exceeds the threshold of
the respective instabilities. These waves are frequently observed in the terrestrial
and planetary magnetosheaths, but their distribution within the magnetosheath is
inhomogeneous and their character varies as a function of location, local and upstream
plasma parameters.
We studied the spatial distribution of the two wave modes in the magnetosheath together
with the local plasma parameters important for the stability of ULF waves. This analysis was
performed on a dataset of all magnetosheath crossings observed by Cluster spacecraft over
two years. For each observation we used bow shock, magnetopause and magnetosheath flow
models to identify the relative position of the spacecraft with respect to magnetosheath
boundaries and local properties of the upstream shock crossing. A strong dependence of
parameters characterizing plasma stability and mirror/AIC wave occurrence on
upstream ΘBn and MA is identified. The occurrence of mirror and AIC modes
was compared against the respective instability thresholds and it was observed
that AIC waves occurred nearly exclusively under mirror stable conditions. This is
interpreted in terms of the different character of non-linear saturation of the two modes. |
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