Articles | Volume 32, issue 12
Ann. Geophys., 32, 1477–1485, 2014
Ann. Geophys., 32, 1477–1485, 2014

Regular paper 08 Dec 2014

Regular paper | 08 Dec 2014

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

H. Breuillard1, O. Agapitov1,2, A. Artemyev1,3, V. Krasnoselskikh1, O. Le Contel4, C. M. Cully5, V. Angelopoulos6, Y. Zaliznyak7, and G. Rolland8 H. Breuillard et al.
  • 1LPC2E/CNRS-University of Orléans, UMR7328, Orléans, France
  • 2National Taras Shevchenko University of Kyiv, Kyiv, Ukraine
  • 3Space Research Institute, RAS, Moscow, Russia
  • 4Laboratoire de Physique des Plasmas, CNRS/Ecole Polytechnique/Sorbonne Universités UPMC/Paris-Sud 11, Saint Maur-des-Fossés, France
  • 5Department of Physics and Astronomy, University of Calgary, Calgary, Alberta, Canada
  • 6Institute of Geophysics and Planetary Physics, Department of Earth and Space Sciences, University of California, Los Angeles, California, USA
  • 7Institute for Nuclear Research, Kyiv, Ukraine
  • 8CNES, Toulouse, France

Abstract. 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.