Journal
JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS
Volume 119, Issue 10, Pages 8288-8298Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1002/2014JA020364
Keywords
chorus; particle-in-cell simulation; HOPE; Van Allen Probes
Categories
Funding
- U.S. Department of Energy
- Defense Threat Reduction Agency
- National Aeronautics and Space Administration
- National Science Foundation
- JHU/APL under NASA [921647, NAS5-01072]
- NSF [AGS-1303300]
- NASA [NNX14AD62G]
- Directorate For Geosciences
- Div Atmospheric & Geospace Sciences [1303300] Funding Source: National Science Foundation
- NASA [685583, NNX14AD62G] Funding Source: Federal RePORTER
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Magnetospheric banded chorus is enhanced whistler waves with frequencies (r)<(e), where (e) is the electron cyclotron frequency, and a characteristic spectral gap at (r)similar or equal to(e)/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 approximate to(e)/2 is a natural consequence of the growth of two whistler modes with different properties.
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