On the origin of falling-tone chorus elements in Earth's inner magnetosphere

H Breuillard (1) , O Agapitov (1, 2) , A Artemyev (1, 3) , V Krasnoselskikh (1) , Olivier Le Contel (4) , C. M. Cully (5) , V Angelopoulos (6) , Y Zaliznyak (7) , G Rolland (8)

1 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace
2 National Taras Shevchenko University of Kyiv
3 IKI - Space Research Institute of the Russian Academy of Sciences
4 LPP - Laboratoire de Physique des Plasmas
5 Department of Physics and Astronomy [Calgary]
6 IGPP - Institute of Geophysics and Planetary Physics [San Diego]
7 Plasma Theory Department
8 CNES - Centre National d'Études Spatiales [Toulouse]

Generation of extremely/very low frequency (ELF/VLF) chorus waves in Earth's inner magnetosphere has received increased attention recently because of their significance for radiation belt dynamics. Though past theoretical and numerical models have demonstrated how rising-tone chorus elements are produced, falling-tone chorus element generation has yet to be explained. Our new model proposes that weak-amplitude falling-tone chorus elements can be generated by magnetospheric reflection of rising-tone elements. Using ray tracing in a realistic plasma model of the inner magnetosphere, we demonstrate that rising-tone elements originating at the magnetic equator propagate to higher latitudes. Upon reflection there, they propagate to lower L-shells and turn into oblique falling tones of reduced power, frequency, and bandwidth relative to their progenitor rising tones. Our results are in good agreement with comprehensive statistical studies of such waves, notably using magnetic field measurements from THEMIS (Time History of Events and Macroscale Interactions during Substorms) spacecraft. Thus, we conclude that the proposed mechanism can be responsible for the generation of weak-amplitude falling-tone chorus emissions.

Domains: Sciences of the Universe [physics]

H Breuillard, O Agapitov, A Artemyev, V Krasnoselskikh, Olivier Le Contel, et al.. On the origin of falling-tone chorus elements in Earth's inner magnetosphere. Annales Geophysicae, 2014, 32, pp.1477-1485. ⟨10.5194/angeo-32-1477-2014⟩. ⟨insu-01173980⟩