title: Ultra-low-frequency wave-driven diffusion of radiation belt relativistic electrons.
abstract: Van Allen radiation belts are typically two zones of energetic particles encircling the Earth separated by the slot region. How the outer radiation belt electrons are accelerated to relativistic energies remains an unanswered question. Recent studies have presented compelling evidence for the local acceleration by very-low-frequency (VLF) chorus waves. However, there has been a competing theory to the local acceleration, radial diffusion by ultra-low-frequency (ULF) waves, whose importance has not yet been determined definitively. Here we report a unique radiation belt event with intense ULF waves but no detectable VLF chorus waves. Our results demonstrate that the ULF waves moved the inner edge of the outer radiation belt earthward 0.3 Earth radii and enhanced the relativistic electron fluxes by up to one order of magnitude near the slot region within about 10 h, providing strong evidence for the radial diffusion of radiation belt relativistic electrons.
authors.affiliation: CAS Key Laboratory of Geospace Environment, Department of Geophysics and Planetary Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China.|Collaborative Innovation Center of Astronautical Science and Technology, University of Science and Technology of China, Hefei, Anhui 230026, China.
authors.forename: Zhenpeng
authors.identifier: http://orcid.org/0000-0001-5577-4538
authors.initials: Z
authors.lastname: Su
authors.affiliation: CAS Key Laboratory of Geospace Environment, Department of Geophysics and Planetary Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China.|Mengcheng National Geophysical Observatory, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Zhu
authors.affiliation: School of Physics and Electronic Sciences, Changsha University of Science and Technology, Changsha Hunan 410004, China.
authors.forename: Fuliang
authors.initials: F
authors.lastname: Xiao
authors.affiliation: Institute of Space Physics and Applied Technology, Peking University, Beijing 100871, China.
authors.forename: Q-G
authors.initials: QG
authors.lastname: Zong
authors.affiliation: Institute of Space Physics and Applied Technology, Peking University, Beijing 100871, China.
authors.forename: X-Z
authors.initials: XZ
authors.lastname: Zhou
authors.affiliation: CAS Key Laboratory of Geospace Environment, Department of Geophysics and Planetary Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China.|Collaborative Innovation Center of Astronautical Science and Technology, University of Science and Technology of China, Hefei, Anhui 230026, China.
authors.forename: Huinan
authors.initials: H
authors.lastname: Zheng
authors.affiliation: CAS Key Laboratory of Geospace Environment, Department of Geophysics and Planetary Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China.|Collaborative Innovation Center of Astronautical Science and Technology, University of Science and Technology of China, Hefei, Anhui 230026, China.|Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China.
authors.forename: Yuming
authors.identifier: http://orcid.org/0000-0002-8887-3919
authors.initials: Y
authors.lastname: Wang
authors.affiliation: CAS Key Laboratory of Geospace Environment, Department of Geophysics and Planetary Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China.|Collaborative Innovation Center of Astronautical Science and Technology, University of Science and Technology of China, Hefei, Anhui 230026, China.
authors.forename: Shui
authors.initials: S
authors.lastname: Wang
authors.affiliation: Institute of Space Physics and Applied Technology, Peking University, Beijing 100871, China.
authors.forename: Y-X
authors.initials: YX
authors.lastname: Hao
authors.affiliation: CAS Key Laboratory of Geospace Environment, Department of Geophysics and Planetary Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China.|Mengcheng National Geophysical Observatory, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China.
authors.forename: Zhonglei
authors.initials: Z
authors.lastname: Gao
authors.affiliation: Harbin Institute of Technology Shenzhen Graduate School, Shenzhen, Guangdong 518055, China.
authors.forename: Zhaoguo
authors.initials: Z
authors.lastname: He
authors.affiliation: Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, Boulder, Colorado 80303-7814, USA.
authors.forename: D N
authors.initials: DN
authors.lastname: Baker
authors.affiliation: Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, New Hampshire 03824-3525, USA.
authors.forename: H E
authors.initials: HE
authors.lastname: Spence
authors.affiliation: Space Science and Applications Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87544, USA.
authors.forename: G D
authors.initials: GD
authors.lastname: Reeves
authors.affiliation: The Aerospace Corporation, Los Angeles, California 90245-4609, USA.
authors.forename: J B
authors.initials: JB
authors.lastname: Blake
authors.affiliation: School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: J R
authors.initials: JR
authors.lastname: Wygant