Bibliography

The Response of the Energy Content of the Outer Electron Radiation Belt to Geomagnetic Storms

Using the data from the Van Allen Probe-A spacecraft, the variability of the total outer radiation belt (2.5300 keV) is investigated for the first time during 51 isolated storms spanning from October 2012 to May 2017. The statistical results show that the TRBEEC exhibits no-change in 20\% of the storms and gets enhanced during 80\% of them. The sub-relativistic electrons (300-500 keV) and relativistic electrons (0.5-2.0 MeV) equally contribute to the TRBEEC during the main phases, while in the recovery phases, the relativistic electrons contribute up to 80\% of the TRBEEC. The results of the superposed epoch analysis of the solar wind parameters and geomagnetic indices indicate that the TRBEEC enhancement events preferably occur during the prolonged southward IMF period when the solar wind-magnetosphere coupling is more efficient. Meanwhile, the high AE index with intense injections of several hundreds of keV \textquotedblleftseed\textquotedblright electrons also favors the increase of the TRBEEC. Case study shows that there is a localized growing PSD (phase space density) peak around L*=4.3 and the chorus wave energy and the gain of TRBEEC are on the same order of magnitude, which may suggest that the enhancement of the TRBEEC is the consequence of the chorus acceleration. Understanding the energy budget of the outer zone electrons can provide more insight into the energy transfer from plasma waves to the energetic electron population, especially for revealing the underlying physics of the energization of outer radiation belt electrons via chorus wave acceleration.

Xiong, Ying; Xie, Lun; Chen, Lunjin; Ni, Binbin; Fu, Suiyan; Pu, Zuyin;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2018

YEAR: 2018     DOI: 10.1029/2018JA025475

Chorus wave; energetic particles; energy content; magnetic storm; outer radiation belt; Van Allen Probes

Multiple-satellite observation of magnetic dip event during the substorm on 10 October, 2013

We present a multiple-satellite observation of the magnetic dip event during the substorm on October 10, 2013. The observation illustrates the temporal and spatial evolution of the magnetic dip and gives a compelling evidence that ring current ions induce the magnetic dip by enhanced plasma beta. The dip moves with the energetic ions in a comparable drift velocity and affects the dynamics of relativistic electrons in the radiation belt. In addition, the magnetic dip provides a favorable condition for the EMIC wave generation based on the linear theory analysis. The calculated proton diffusion coefficients show that the observed EMIC wave can lead to the pitch angle scattering losses of the ring current ions, which in turn partially relax the magnetic dip in the observations. This study enriches our understanding of magnetic dip evolution and demonstrates the important role of the magnetic dip for the coupling of radiation belt and ring current.

He, Zhaoguo; Chen, Lunjin; Zhu, Hui; Xia, Zhiyang; Reeves, G.; Xiong, Ying; Xie, Lun; Cao, Yong;

Published by: Geophysical Research Letters      Published on: 09/2017

YEAR: 2017     DOI: 10.1002/2017GL074869

EMIC wave; magnetic dip; radiation belt electrons; Ring current ions; Van Allen Probes

Relativistic electron\textquoterights butterfly pitch angle distribution modulated by localized background magnetic field perturbation driven by hot ring current ions

Dayside modulated relativistic electron\textquoterights butterfly pitch angle distributions (PADs) from \~200 keV to 2.6 MeV were observed by Van Allen Probe B at L = 5.3 on 15 November 2013. They were associated with localized magnetic dip driven by hot ring current ion (60\textendash100 keV proton and 60\textendash200 keV helium and oxygen) injections. We reproduce the electron\textquoterights butterfly PADs at satellite\textquoterights location using test particle simulation. The simulation results illustrate that a negative radial flux gradient contributes primarily to the formation of the modulated electron\textquoterights butterfly PADs through inward transport due to the inductive electric field, while deceleration due to the inductive electric field and pitch angle change also makes in part contribution. We suggest that localized magnetic field perturbation, which is a frequent phenomenon in the magnetosphere during magnetic disturbances, is of great importance for creating electron\textquoterights butterfly PADs in the Earth\textquoterights radiation belts.

Xiong, Ying; Chen, Lunjin; Xie, Lun; Fu, Suiyan; Xia, Zhiyang; Pu, Zuyin;

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

YEAR: 2017     DOI: 10.1002/2017GL072558

butterfly distribution; Radiation belt; ring current; Van Allen Probes

Oxygen cyclotron harmonic waves observed by the Van Allen Probes

Fine structured multiple-harmonic electromagnetic emissions at frequencies around the equatorial oxygen cyclotron harmonics are observed by Van Allen Probe A outside the core plasmasphere (L~5) off the magnetic equator (MLAT~-7.5\textdegree) during a magnetic storm. We find that the multiple-harmonic emissions have their PSD peaks at 2~8 equatorial oxygen gyro-harmonics (f~nfO+, n=2~8) while the fundamental mode (n=1) is absent, implying that the harmonic waves are generated near the equator and propagate into the observation region. Additionally these electromagnetic emissions are linear polarized. Different from the equatorial noise emission propagating very obliquely, these emissions have moderate wave normal angles (about 40\textdegree~60\textdegree) which predominately become larger as the harmonic number increases. Considering their frequency and wave normal angle characteristics, it is suggested that these multiple-harmonic emissions might play an important role in the dynamic variation of radiation belt electrons.

Xiongdong, Yu; Zhigang, Yuan; Dedong, Wang; Shiyong, Huang; Haimeng, Li; Tao, Yu; Zheng, Qiao;

Published by: Science China: Earth Sciences      Published on: 03/2017

YEAR: 2017     DOI: 10.1007/s11430-016-9024-3

Oxygen Cyclotron Harmonic Waves; Radiation belt; Ring current ions; Van Allen Probes

Responses of relativistic electron fluxes in the outer radiation belt to geomagnetic storms

Geomagnetic storms can either increase or decrease relativistic electron fluxes in the outer radiation belt. A statistical survey of 84 isolated storms demonstrates that geomagnetic storms preferentially decrease relativistic electron fluxes at higher energies, while flux enhancements are more common at lower energies. In about 87\% of the storms, 0.3\textendash2.5 MeV electron fluxes show an increase, whereas 2.5\textendash14 MeV electron fluxes increase in only 35\% of the storms. Superposed epoch analyses suggest that such \textquotedblleftenergy-dependent\textquotedblright responses of electrons preferably occur during conditions of high solar wind density which is favorable to generate magnetospheric electromagnetic ion cyclotron (EMIC) waves, and these events are associated with relatively weaker chorus activities. We have examined one of the cases where observed EMIC waves can resonate effectively with >2.5 MeV electrons and scatter them into the atmosphere. The correlation study further illustrates that electron flux dropouts during storm main phases do not correlate well with the flux buildup during storm recovery phases. We suggest that a combination of efficient EMIC-induced scattering and weaker chorus-driven acceleration provides a viable candidate for the energy-dependent responses of outer radiation belt relativistic electrons to geomagnetic storms. These results are of great interest to both understanding of the radiation belt dynamics and applications in space weather.

Xiong, Ying; Xie, Lun; Pu, Zuyin; Fu, Suiyan; Chen, Lunjin; Ni, Binbin; Li, Wen; Li, Jinxing; Guo, Ruilong; Parks, G.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 11/2015

YEAR: 2015     DOI: 10.1002/2015JA021440

energy dependence; Geomagnetic storm; Radiation belts; relativistic electrons; Solar wind