Observational evidence of generation mechanisms for very oblique lower band chorus using THEMIS waveform data

Abstract : Chorus waves are intense coherent whistler mode waves with frequency chirping which play a dual role in both loss and acceleration of radiation belt electrons in the Earth's magnetosphere. Although the generation of parallel chorus waves has been extensively studied by means of theory, simulations, and observations, the generation mechanism of very oblique chorus waves still remains a mystery. In this study, we have analyzed hundreds of very oblique discrete (rising or falling tone) lower band chorus events collected from 7 years of Time History of Events and Macroscale Interactions during Substorms (THEMIS) waveform data to investigate their potential generation mechanisms. Comparisons between wave normal angles directly measured onboard THEMIS in the dawn-day sector at L = 5–9 and inferred from theoretical models on the basis of measured wave characteristics (frequency sweep rate, mean frequency, and amplitude) show that these very oblique waves are more commonly generated through cyclotron resonance with anisotropic electron streams. However, a second generation mechanism via Landau resonance with low-energy electron beams seems to be also operating on the nightside at L < 6.7 and at all local times at L > 8.5. Moreover, very oblique lower band chorus waves with large frequency chirping rates or small magnetic field amplitudes are more likely excited via cyclotron resonance, while waves with small frequency chirping rates or large magnetic field amplitudes are preferentially generated through Landau resonance. This comprehensive statistical study provides interesting insight into the possible generation mechanisms of very oblique lower band chorus waves in the Earth's magnetosphere.
Type de document :
Article dans une revue
Journal of Geophysical Research : Space Physics, American Geophysical Union/Wiley, 2016, 121 (7), pp.6732 - 6748. 〈10.1002/2016JA022915〉
Liste complète des métadonnées

Littérature citée [65 références]  Voir  Masquer  Télécharger

https://hal-insu.archives-ouvertes.fr/insu-01632588
Contributeur : Nathalie Pothier <>
Soumis le : vendredi 10 novembre 2017 - 14:07:59
Dernière modification le : jeudi 11 janvier 2018 - 06:24:16
Document(s) archivé(s) le : dimanche 11 février 2018 - 14:09:59

Fichier

Gao_et_al-2016-Journal_of_Geop...
Fichiers éditeurs autorisés sur une archive ouverte

Identifiants

Collections

Citation

Xinliang Gao, Didier Mourenas, Wen Li, Anton Artemyev, Quanming Lu, et al.. Observational evidence of generation mechanisms for very oblique lower band chorus using THEMIS waveform data. Journal of Geophysical Research : Space Physics, American Geophysical Union/Wiley, 2016, 121 (7), pp.6732 - 6748. 〈10.1002/2016JA022915〉. 〈insu-01632588〉

Partager

Métriques

Consultations de la notice

55

Téléchargements de fichiers

25