Bibliography

Generation of lower and upper bands of electrostatic electron cyclotron harmonic waves in the Van Allen radiation belts

Electrostatic electron cyclotron harmonic (ECH) waves generated by the electron loss cone distribution can produce efficient scattering loss of plasma sheet electrons, which has a significant effect on the dynamics in the outer magnetosphere. Here we report two ECH emission events around the same location L≈ 5.7\textendash5.8, MLT ≈ 12 from Van Allen Probes on 11 February (event A) and 9 January 2014 (event B), respectively. The spectrum of ECH waves was centered at the lower half of the harmonic bands during event A, but the upper half during event B. The observed electron phase space density in both events is fitted by the subtracted bi-Maxwellian distribution, and the fitting functions are used to evaluate the local growth rates of ECH waves based on a linear theory for homogeneous plasmas. ECH waves are excited by the loss cone instability of 50 eV\textendash1 keV electrons in the lower half of harmonic bands in the low-density plasmasphere in event A, and 1\textendash10 keV electrons in the upper half of harmonic bands in a relatively high-density region in event B. The current results successfully explain observations and provide a first direct evidence on how ECH waves are generated in the lower and upper half of harmonic frequency bands.

Zhou, Qinghua; Xiao, Fuliang; Yang, Chang; Liu, Si; He, Yihua; Baker, D.; Spence, H.; Reeves, G.; Funsten, H.;

Published by: Geophysical Research Letters      Published on: 05/2017

YEAR: 2017     DOI: 10.1002/2017GL073051

ECH waves; RBSP results; Van Allen Probes; Wave-particle interaction

Generation of extremely low frequency chorus in Van Allen radiation belts

Recent studies have shown that chorus can efficiently accelerate the outer radiation belt electrons to relativistic energies. Chorus, previously often observed above 0.1 equatorial electron gyrofrequency fce, was generated by energetic electrons originating from Earth\textquoterights plasma sheet. Chorus below 0.1 fce has seldom been reported until the recent data from Van Allen Probes, but its origin has not been revealed so far. Because electron resonant energy can approach the relativistic level at extremely low frequency, relativistic effects should be considered in the formula for whistler mode wave growth rate. Here we report high-resolution observations during the 14 October 2014 small storm and firstly demonstrate, using a fully relativistic simulation, that electrons with the high-energy tail population and relativistic pitch angle anisotropy can provide free energy sufficient for generating chorus below 0.1 fce. The simulated wave growth displays a very similar pattern to the observations. The current results can be applied to Jupiter, Saturn, and other magnetized planets.

Xiao, Fuliang; Liu, Si; Tao, Xin; Su, Zhenpeng; Zhou, Qinghua; Yang, Chang; He, Zhaoguo; He, Yihua; Gao, Zhonglei; Baker, D.; Spence, H.; Reeves, G.; Funsten, H.; Blake, J.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 03/2017

YEAR: 2017     DOI: 10.1002/2016JA023561

ELF chorus waves; RBSP results; relativistic distribution; Van Allen Probes; Wave-particle interaction

Evolution of chorus emissions into plasmaspheric hiss observed by Van Allen Probes

The two classes of whistler mode waves (chorus and hiss) play different roles in the dynamics of radiation belt energetic electrons. Chorus can efficiently accelerate energetic electrons, and hiss is responsible for the loss of energetic electrons. Previous studies have proposed that chorus is the source of plasmaspheric hiss, but this still requires an observational confirmation because the previously observed chorus and hiss emissions were not in the same frequency range in the same time. Here we report simultaneous observations form Van Allen Probes that chorus and hiss emissions occurred in the same range \~300\textendash1500 Hz with the peak wave power density about 10-5 nT2/Hz during a weak storm on 3 July 2014. Chorus emissions propagate in a broad region outside the plasmapause. Meanwhile, hiss emissions are confined inside the plasmasphere, with a higher intensity and a broader area at a lower frequency. A sum of bi-Maxwellian distribution is used to model the observed anisotropic electron distributions and to evaluate the instability of waves. A three-dimensional ray tracing simulation shows that a portion of chorus emission outside the plasmasphere can propagate into the plasmasphere and evolve into plasmaspheric hiss. Moreover, hiss waves below 1 kHz are more intense and propagate over a broader area than those above 1 kHz, consistent with the observation. The current results can explain distributions of the observed hiss emission and provide a further support for the mechanism of evolution of chorus into hiss emissions.

Zhou, Qinghua; Xiao, Fuliang; Yang, Chang; Liu, Si; He, Yihua; Wygant, J.; Baker, D.; Spence, H.; Reeves, G.; Funsten, H.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 05/2016

YEAR: 2016     DOI: 10.1002/2016JA022366

chorus waves; Plasmaspheric Hiss; RBSP results; Van Allen Probes

Excitation of nightside magnetosonic waves observed by Van Allen Probes

During the recovery phase of the geomagnetic storm on 30-31 March 2013, Van Allen Probe A detected enhanced magnetosonic (MS) waves in a broad range of L =1.8-4.7 and MLT =17-22 h, with a frequency range ~10-100 Hz. In the meanwhile, distinct proton ring distributions with peaks at energies of ~10 keV, were also observed in L =3.2-4.6 and L =5.0-5.6. Using a subtracted bi-Maxwellian distribution to model the observed proton ring distribution, we perform three dimensional ray tracing to investigate the instability, propagation and spatial distribution of MS waves. Numerical results show that nightside MS waves are produced by proton ring distribution and grow rapidly from the source location L =5.6 to the location L =5.0, but remain nearly stable at locations L <5.0 Moreover, waves launched toward lower L-shells with different initial azimuthal angles propagate across different MLT regions with divergent paths at first, then gradually turn back toward higher L-shells and propagate across different MLT regions with convergent paths. The current results further reveal that MS waves are generated by a ring distribution of ~10 keV proton and proton ring in one region can contribute to the MS wave power in another region.

Zhou, Qinghua; Xiao, Fuliang; Yang, Chang; Liu, Si; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.; Funsten, H.; Blake, J.; Baker, D.; Wygant, J.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 11/2014

YEAR: 2014     DOI: 10.1002/2014JA020481

magnetosonic wave; RBSP results; Van Allen Probes; Wave-particle interaction