Wave-induced loss of ultra-relativistic electrons in the Van Allen radiation belts

Yuri Y Shprits; Alexander Y Drozdov; Maria Spasojevic; Adam C Kellerman; Maria E Usanova; Mark J Engebretson; Oleksiy V Agapitov; Irina S Zhelavskaya; Tero J Raita; Harlan E Spence; Daniel N Baker; Hui Zhu; Nikita A Aseev

doi:10.1038/ncomms12883

Wave-induced loss of ultra-relativistic electrons in the Van Allen radiation belts

Nat Commun. 2016 Sep 28:7:12883. doi: 10.1038/ncomms12883.

Authors

Yuri Y Shprits^{1

2

3}, Alexander Y Drozdov², Maria Spasojevic⁴, Adam C Kellerman², Maria E Usanova⁵, Mark J Engebretson⁶, Oleksiy V Agapitov^{7

8}, Irina S Zhelavskaya¹, Tero J Raita⁹, Harlan E Spence¹⁰, Daniel N Baker⁵, Hui Zhu², Nikita A Aseev¹

Affiliations

¹ Helmholtz Centre Potsdam, GFZ, German Research Centre For Geosciences, Section 2.3, Building K 3, Room 012, Potsdam 14467, Germany.
² Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California 90095-1567, USA.
³ Universität Potsdam, Institut für Physik und Astronomie, Potsdam 14476, Germany.
⁴ Department of Electrical Engineering, Stanford University, Stanford, California 94305-9505, USA.
⁵ Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, Boulder, Colorado 80303, USA.
⁶ Physics Department, Augsburg College, Minneapolis, Minnesota 55454, USA.
⁷ Space Sciences Laboratory, University of California, Berkeley, California 94720, USA.
⁸ Natilonal Taras Shevchenko University of Kyiv, Kyiv 01033, Ukraine.
⁹ Sodankylä Geophysical Observatory, Sodankylä, Finland and University of Oulu, Oulu 99600, Finland.
¹⁰ Institute for the Study of Earth Oceans and Space, University of New Hampshire, Durham, New Hampshire 03824-3525, USA.

Abstract

The dipole configuration of the Earth's magnetic field allows for the trapping of highly energetic particles, which form the radiation belts. Although significant advances have been made in understanding the acceleration mechanisms in the radiation belts, the loss processes remain poorly understood. Unique observations on 17 January 2013 provide detailed information throughout the belts on the energy spectrum and pitch angle (angle between the velocity of a particle and the magnetic field) distribution of electrons up to ultra-relativistic energies. Here we show that although relativistic electrons are enhanced, ultra-relativistic electrons become depleted and distributions of particles show very clear telltale signatures of electromagnetic ion cyclotron wave-induced loss. Comparisons between observations and modelling of the evolution of the electron flux and pitch angle show that electromagnetic ion cyclotron waves provide the dominant loss mechanism at ultra-relativistic energies and produce a profound dropout of the ultra-relativistic radiation belt fluxes.