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Van Allen Probes observation and modeling of chorus excitation and propagation during weak geomagnetic activities
Author(s) -
He Yihua,
Xiao Fuliang,
Zhou Qinghua,
Yang Chang,
Liu Si,
Baker D. N.,
Kletzing C. A.,
Kurth W. S.,
Hospodarsky G. B.,
Spence H. E.,
Reeves G. D.,
Funsten H. O.,
Blake J. B.
Publication year - 2015
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2015ja021376
Subject(s) - chorus , physics , geomagnetic storm , van allen probes , earth's magnetic field , electron , interplanetary spaceflight , geophysics , computational physics , anisotropy , magnetosphere , astrophysics , magnetic field , atmospheric sciences , atomic physics , solar wind , van allen radiation belt , optics , nuclear physics , art , literature , quantum mechanics
Abstract We report correlated data on nightside chorus waves and energetic electrons during two small storm periods: 1 November 2012 ( D s t ≈−45) and 14 January 2013 ( D s t ≈−18). The Van Allen Probes simultaneously observed strong chorus waves at locations L = 5.8–6.3, with a lower frequency band 0.1–0.5 f ce and a peak spectral density ∼10 −4 nT 2 /Hz. In the same period, the fluxes and anisotropy of energetic (∼10–300 keV) electrons were greatly enhanced in the interval of large negative interplanetary magnetic field B z . Using a bi‐Maxwellian distribution to model the observed electron distribution, we perform ray tracing simulations to show that nightside chorus waves are indeed produced by the observed electron distribution with a peak growth for a field‐aligned propagation approximately between 0.3 f ce and 0.4 f ce , at latitude <7°. Moreover, chorus waves launched with initial normal angles either θ <90° or >90° propagate along the field either northward or southward and then bounce back either away from Earth for a lower frequency or toward Earth for higher frequencies. The current results indicate that nightside chorus waves can be excited even during weak geomagnetic activities in cases of continuous injection associated with negative B z . Moreover, we examine a dayside event during a small storm C on 8 May 2014 ( D s t ≈−45) and find that the observed anisotropic energetic electron distributions potentially contribute to the generation of dayside chorus waves, but this requires more thorough studies in the future.