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| Titel |
Global distribution of ion temperature and ULF wave activity in the magnetosheath from joint Cluster and THEMIS observations |
| VerfasserIn |
J. Soucek, C. P. Escoubet |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250060835
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| Zusammenfassung |
| We present a multi-spacecraft statistical study of the terrestrial magnetosheath, focusing on
large scale asymmetry in plasma parameters and properties of associated low frequency
plasma waves. The study is based on conjunction events when Cluster and THEMIS
spacecraft were simultaneously sampling opposite flanks of the magnetosheath. We show that
ion temperature anisotropy T-¥-T|| is often strongly asymmetric with respect to the
Sun-Earth line. Tracing the plasma flow from the spacecraft location back to the bow
shock suggests that the ion temperature anisotropy depends strongly on the local
shock parameters (shock strength and the angle ÎBN between shock normal and
upstream magnetic field) even relatively deep in the magnetosheath. The global
distribution of the ion temperature itself is however more symmetric and shows less
dependence on ÎBN. We also investigated the asymmetry and spatial distribution
of the occurrence of mirror and ion-cyclotron waves in different regions of the
magnetosheath. The Alfvèn-ion-cyclotron (AIC) waves are found to be the dominant low
frequency mode in the magnetosheath region close to to the bow shock. Mirror mode
structures are more frequently observed deeper inside the magnetosheath, from
intermediate radial distances to the magnetopause. The transition between regions
dominated by AIC and mirror waves also depends strongly on ÎBN parameter of the
associated bow shock. The statistical results are compared to the predictions of
Rankine-Hugoniot relations and thresholds of ion-cyclotron and mirror instabilities. |
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