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Conference papers

Whistler Waves and the Halo Electron Anisotropies in the Inner Heliosphere: Helios Observations

Abstract : We present the analysis of narrow-band whistler waves observed in the 10-200 Hz frequency range in the inner heliosphere (0.3 to 1 AU). These whistlers are identified from the spectral density of the AC magnetic field as measured by the search-coil magnetometer on-board the HELIOS 1 spacecraft. We have studied the radial evolution of these whistlers for different physical parameters such as solar wind type and the features associated with the electron distribution function. We find that the majority of whistlers are observed in the slow (< 500 kms-1) solar wind. In the fast (> 600 kms-1) wind whistler activity is significantly lower. We observe that occurrence rate of whistlers increases both in the slow and fast wind as we move away from the Sun. Knowing that a high halo anisotropy (Th⊥/Th∥) offers better conditions for whistler generation through instabilities (both heat-flux and anisotropy), we have studied the variation of the halo anisotropy in the inner heliosphere. We find that in the slow wind the anisotropy is higher than in fast wind, and also that it increases radially in both types of winds. These observations explain that the conditions for whistler generation are better met in the slow wind and improve with radial distance. We hypothesize the existence of a feedback mechanism to explain the observed radial variations of occurrence rate of whistlers in relation with the halo anisotropy.
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https://hal-insu.archives-ouvertes.fr/insu-03562459
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Submitted on : Wednesday, February 9, 2022 - 7:26:31 AM
Last modification on : Tuesday, May 10, 2022 - 3:24:57 PM

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V. K. Jagarlamudi, O. Alexandrova, L. Bercic, Thierry Dudok de Wit, V. Krasnoselskikh, et al.. Whistler Waves and the Halo Electron Anisotropies in the Inner Heliosphere: Helios Observations. American Geophysical Union, 2019, San Francisco, United States. 15 pp. ⟨insu-03562459⟩

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