title: Whistler anisotropy instabilities as the source of banded chorus: Van Allen Probes observations and particle-in-cell simulations.
abstract: Magnetospheric banded chorus is enhanced whistler waves with frequenciesωr<Ωe, where Ωeis the electron cyclotron frequency, and a characteristic spectral gap atωr≃Ωe/2. This paper uses spacecraft observations and two-dimensional particle-in-cell simulations in a magnetized, homogeneous, collisionless plasma to test the hypothesis that banded chorus is due to local linear growth of two branches of the whistler anisotropy instability excited by two distinct, anisotropic electron components of significantly different temperatures. The electron densities and temperatures are derived from Helium, Oxygen, Proton, and Electron instrument measurements on the Van Allen Probes A satellite during a banded chorus event on 1 November 2012. The observations are consistent with a three-component electron model consisting of a cold (a few tens of eV) population, a warm (a few hundred eV) anisotropic population, and a hot (a few keV) anisotropic population. The simulations use plasma and field parameters as measured from the satellite during this event except for two numbers: the anisotropies of the warm and the hot electron components are enhanced over the measured values in order to obtain relatively rapid instability growth. The simulations show that the warm component drives the quasi-electrostatic upper band chorus and that the hot component drives the electromagnetic lower band chorus; the gap at ∼Ωe/2 is a natural consequence of the growth of two whistler modes with different properties.
authors.affiliation: Los Alamos National Laboratory Los Alamos, New Mexico, USA.
authors.forename: Xiangrong
authors.initials: X
authors.lastname: Fu
authors.affiliation: Los Alamos National Laboratory Los Alamos, New Mexico, USA.
authors.forename: Misa M
authors.initials: MM
authors.lastname: Cowee
authors.affiliation: Los Alamos National Laboratory Los Alamos, New Mexico, USA.
authors.forename: Reinhard H
authors.initials: RH
authors.lastname: Friedel
authors.affiliation: Los Alamos National Laboratory Los Alamos, New Mexico, USA.
authors.forename: Herbert O
authors.initials: HO
authors.lastname: Funsten
authors.affiliation: Space Science Institute Boulder, Colorado, USA.
authors.forename: S Peter
authors.initials: SP
authors.lastname: Gary
authors.affiliation: Department of Physics and Astronomy, University of Iowa Iowa City, Iowa, USA.
authors.forename: George B
authors.initials: GB
authors.lastname: Hospodarsky
authors.affiliation: Department of Physics and Astronomy, University of Iowa Iowa City, Iowa, USA.
authors.forename: Craig
authors.initials: C
authors.lastname: Kletzing
authors.affiliation: Department of Physics and Astronomy, University of Iowa Iowa City, Iowa, USA.
authors.forename: William
authors.initials: W
authors.lastname: Kurth
authors.affiliation: Los Alamos National Laboratory Los Alamos, New Mexico, USA.
authors.forename: Brian A
authors.initials: BA
authors.lastname: Larsen
authors.affiliation: Department of Physics, Auburn University Auburn, Alabama, USA.
authors.forename: Kaijun
authors.initials: K
authors.lastname: Liu
authors.affiliation: NASA/Goddard Space Flight Center Greenbelt, Maryland, USA.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: MacDonald
authors.affiliation: Department of Physics, Auburn University Auburn, Alabama, USA.
authors.forename: Kyungguk
authors.initials: K
authors.lastname: Min
authors.affiliation: Los Alamos National Laboratory Los Alamos, New Mexico, USA.
authors.forename: Geoffrey D
authors.initials: GD
authors.lastname: Reeves
authors.affiliation: Los Alamos National Laboratory Los Alamos, New Mexico, USA.
authors.forename: Ruth M
authors.initials: RM
authors.lastname: Skoug
authors.affiliation: Los Alamos National Laboratory Los Alamos, New Mexico, USA.
authors.forename: Dan
authors.initials: D
authors.lastname: Winske
keywords: HOPE; Van Allen Probes; chorus; particle-in-cell simulation