title: Rapid local acceleration of relativistic radiation-belt electrons by magnetospheric chorus.
abstract: Recent analysis of satellite data obtained during the 9 October 2012 geomagnetic storm identified the development of peaks in electron phase space density, which are compelling evidence for local electron acceleration in the heart of the outer radiation belt, but are inconsistent with acceleration by inward radial diffusive transport. However, the precise physical mechanism responsible for the acceleration on 9 October was not identified. Previous modelling has indicated that a magnetospheric electromagnetic emission known as chorus could be a potential candidate for local electron acceleration, but a definitive resolution of the importance of chorus for radiation-belt acceleration was not possible because of limitations in the energy range and resolution of previous electron observations and the lack of a dynamic global wave model. Here we report high-resolution electron observations obtained during the 9 October storm and demonstrate, using a two-dimensional simulation performed with a recently developed time-varying data-driven model, that chorus scattering explains the temporal evolution of both the energy and angular distribution of the observed relativistic electron flux increase. Our detailed modelling demonstrates the remarkable efficiency of wave acceleration in the Earth's outer radiation belt, and the results presented have potential application to Jupiter, Saturn and other magnetized astrophysical objects.
authors.affiliation: Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California 90095-1565, USA.
authors.forename: R M
authors.initials: RM
authors.lastname: Thorne
authors.affiliation: Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California 90095-1565, USA.
authors.forename: W
authors.initials: W
authors.lastname: Li
authors.affiliation: Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California 90095-1565, USA.
authors.forename: B
authors.initials: B
authors.lastname: Ni
authors.affiliation: Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California 90095-1565, USA.
authors.forename: Q
authors.initials: Q
authors.lastname: Ma
authors.affiliation: Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California 90095-1565, USA.
authors.forename: J
authors.initials: J
authors.lastname: Bortnik
authors.affiliation: Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California 90095-1565, USA.
authors.forename: L
authors.initials: L
authors.lastname: Chen
authors.affiliation: Laboratory for Atmospheric and Space Research, University of Colorado, Boulder, Colorado 80303-7814, USA.
authors.forename: D N
authors.initials: DN
authors.lastname: Baker
authors.affiliation: Each 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: Space Science and Applications Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87544, USA.
authors.forename: M G
authors.initials: MG
authors.lastname: Henderson
authors.affiliation: Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242-1479, USA.
authors.forename: C A
authors.initials: CA
authors.lastname: Kletzing
authors.affiliation: Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242-1479, USA.
authors.forename: W S
authors.initials: WS
authors.lastname: Kurth
authors.affiliation: Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242-1479, USA.
authors.forename: G B
authors.initials: GB
authors.lastname: Hospodarsky
authors.affiliation: The Aerospace Corporation, Los Angeles, California 90245-4609, USA.
authors.forename: J B
authors.initials: JB
authors.lastname: Blake
authors.affiliation: The Aerospace Corporation, Los Angeles, California 90245-4609, USA.
authors.forename: J F
authors.initials: JF
authors.lastname: Fennell
authors.affiliation: The Aerospace Corporation, Los Angeles, California 90245-4609, USA.
authors.forename: S G
authors.initials: SG
authors.lastname: Claudepierre
authors.affiliation: NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA.
authors.forename: S G
authors.initials: SG
authors.lastname: Kanekal