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Artificial modification of Earth's radiation belts by ground-based very-low-frequency(VLF)transmitters

Science China Earth Sciences 2022年第3期65卷 391-413页

作者： Binbin NI Man HUA Xudong GU Song FU Zheng XIANG Xing CAO Xin MA Department of Space Physics School of Electronic InformationWuhan UniversityWuhan 430072China Chinese Academy of Sciences Center for Excellence in Comparative Planetology Hefei 230026China

wave-particle interactions play a fundamental role in the dynamic variability of Earth’s donut-shaped radiation belts that are highly populated by magnetically trapped energetic particles and characteristically separated by the slot devoid of high energetic electrons.Owing to the continuous accumulation of high-quality wave and particle measurements from multiple satellites in geospace,the important contribution of ground-based very-low-frequency(VLF)transmitter waves to the electron dynamics in the near-Earth space has been unprecedently advanced,in addition to those established findings of the significant effects of a variety of naturally occurring magnetospheric waves.This paper focuses on the artificial modification of Earth’s inner radiation belt and slot by artificial VLF transmitter emissions.We review the global distributions of VLF transmitter waves in geospace,their scattering effects on radiation belt electrons in terms of both theoretical and observational analyses,and diffusion simulation results of wave-particle interactions along with data-model comparisons.We start with a brief review of the radiation belt electron dynamics and an introduction of anthropogenic VLF transmitter waves.Subsequently,we review the global morphology of in situ VLF transmitter waves corresponding to different transmitter locations,including their day-night asymmetry,geographic distributions,seasonal and geomagnetic activity dependence,and wave propagation features.Existed theoretical and observational analyses of electron scattering effects by VLF transmitter waves are then reviewed to approach the underlying physics that can modulate the spatio-temporal variations of the electron radiation belts.Further Fokker-Planck electron diffusion simulations and their comparisons with realistic satellite observations clearly indicate that VLF transmitter emissions can effectively remove energetic electrons to produce a radially bifurcated electron belt,thereby quantitatively confirming the direct link between operations of VLF tran

关键词： VLF transmitters wave-particle interactions Electron precipitation Earth’s radiation belts Flux bifurcation

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Test particle simulations of resonant interactions between energetic electrons and discrete, multi-frequency artificial whistler waves in the plasmasphere

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Chinese Physics B 2014年第8期23卷 678-686页

作者：常珊珊倪彬彬赵正予顾旭东周晨 Department of Space Physics School of Electronic Information Wuhan University

Modulated high frequency （HF） heating of the ionosphere provides a feasible means of artificially generating ex- tremely low frequency （ELF）/very low frequency （VLF） whistler waves, which can leak into the inner magnetosphere and contribute to resonant interactions with high energy electrons. Combining the ray tracing method and test particle simulations, we evaluate the effects of energetic electron resonant scattering driven by the discrete, multi-frequency arti- ficially generated ELF/VLF waves. The simulation results indicate a stochastic behavior of electrons and a linear profile of pitch angle and kinetic energy variations averaged over all test electrons. These features are similar to those associated with single-frequency waves. The computed local diffusion coefficients show that, although the momentum diffusion of relativistic electrons due to artificial ELF/VLF whistlers with a nominal amplitude of ~ 1 pT is minor, the pitch angle scattering can be notably efficient at low pitch angles near the loss cone, which supports the feasibility of artificial triggering of multi-frequency ELF/VLF whistler waves for the removal of high energy electrons from the magnetosphere. We also investigate the dependences of diffusion coefficients on the frequency interval （△f） of the discrete, multi-frequency waves. We find that there is a threshold value of Af for which the net diffusion coefficient of multi-frequency whistlers is inversely proportional to △f （proportional to the frequency components Nw） when △f is below the threshold value but it remains unchanged with increasing Af when △f is larger than the threshold value. This is explained as being due to the fact that the resonant scattering effect of broadband waves is the sum of the effects of each frequency in the ＇effective frequency band＇. Our results suggest that the modulation frequency of HF heating of the ionosphere can be appropriately selected with reasonable frequency intervals so that better performance of controlled precipitation of high energy electron

关键词： wave-particle interactions test particle simulations discrete multi-frequency whistler waves,ionospheric modification

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Identification of ring current proton precipitation driven by scattering of electromagnetic ion cyclotron waves

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Fundamental Research 2023年第2期3卷 257-264页

作者： Binbin Ni Yang Zhang Xudong Gu Department of Space Physics School of Electronic InformationWuhan UniversityWuhanHubei 430072China CAS Center for Excellence in Comparative Planetology Hefei 230026China MNR Key Laboratory for Polar Science Polar Research Institute of ChinaShanghai 200136China

Among the most intense emissions in the Earth's magnetosphere,electromagnetic ion cyclotron(EMIC)waves are regarded as a critical candidate contributing to the precipitation losses of ring current protons,which however lacks direct multi-point observations to establish the underlying physical connection.Based upon a robust conjunction between the satellite pair of Van Allen Probe B and NOAA-19,we perform a detailed analysis to capture simultaneous enhancements of EMIC waves and ring current proton precipitation.By assuming that the ring current proton precipitation is mainly caused by EMIC wave scattering,we establish a physical model between the wave-driven proton diffusion and the ratio of precipitated-to-trapped proton count rates,which is subsequently applied to infer the intensity of EMIC waves required to cause the observed proton precipitation.Our simulations indicate that the model results of EMIC wave intensity,obtained using either the observed or empirical Gaussian wave frequency spectrum,are consistent with the wave observations,within a factor of 1.5.Our study therefore strongly supports the dominant contribution of EMIC waves to the ring current proton precipitation,and offers a valuable means to construct the global profile of EMIC wave intensity using low-altitude NOAA POES proton measurements,which generally have a broad L-shell coverage and high time resolution in favor of near-real-time conversion of the global EMIC wave distribution.

关键词： Electromagnetic ion cyclotron waves Ring current protons wave-particle interactions Conjugate observations Precipitation losses

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On the loss mechanisms of radiation belt electron dropouts during the 12 September 2014 geomagnetic storm

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Earth and Planetary Physics 2020年第6期4卷 598-610页

作者： Xin Ma Zheng Xiang BinBin Ni Song Fu Xing Cao Man Hua DeYu Guo YingJie Guo XuDong Gu ZeYuan Liu Qi Zhu Department of Space Physics School of Electronic InformationWuhan UniversityWuhan 430072China Chinese Academy of Sciences Center for Excellence in Comparative Planetology Hefei 230026China

Radiation belt electron dropouts indicate electron flux decay to the background level during geomagnetic storms,which is commonly attributed to the effects of wave-induced pitch angle scattering and magnetopause shadowing.To investigate the loss mechanisms of radiation belt electron dropouts triggered by a solar wind dynamic pressure pulse event on 12 September 2014,we comprehensively analyzed the particle and wave measurements from Van Allen Probes.The dropout event was divided into three periods:before the storm,the initial phase of the storm,and the main phase of the storm.The electron pitch angle distributions(PADs)and electron flux dropouts during the initial and main phases of this storm were investigated,and the evolution of the radial profile of electron phase space density(PSD)and the(μ,K)dependence of electron PSD dropouts(whereμ,K,and L^*are the three adiabatic invariants)were analyzed.The energy-independent decay of electrons at L>4.5 was accompanied by butterfly PADs,suggesting that the magnetopause shadowing process may be the major loss mechanism during the initial phase of the storm at L>4.5.The features of electron dropouts and 90°-peaked PADs were observed only for>1 MeV electrons at Lwave-induced scattering effect may dominate the electron loss processes at the lower L-shell during the main phase of the storm.Evaluations of the(μ,K)dependence of electron PSD drops and calculations of the minimum electron resonant energies of H+-band electromagnetic ion cyclotron(EMIC)waves support the scenario that the observed PSD drop peaks around L^*=3.9 may be caused mainly by the scattering of EMIC waves,whereas the drop peaks around L^*=4.6 may result from a combination of EMIC wave scattering and outward radial diffusion.

关键词： radiation belt electron flux dropouts geomagnetic storm electron phase space density magnetopause shadowing wave-particle interactions

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Effect of kappa distribution on the damping rate of the obliquely propagating magnetosonic mode

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Plasma Science and Technology 2018年第3期20卷 43-48页

作者： Imran Ali KHAN G MURTAZA Department of Physics G. C. University Lahore Katchery Road 54000 Lahore Pakistan

Data from spacecrafts suggest that space plasma has an abundance of suprathermal particles which are controlled by the spectral index κ when modeled on kappa particle velocity distribution. In this paper, considering homogeneous plasma, the effect of integer values of κ on the damping rate of an obliquely propagating magnetosonic（MS） wave is studied. The frequency of the MS wave is assumed to be less than ion cyclotron frequency, i.e.,iw（28）w. Under this assumption, the dispersion relation is investigated both numerically and analytically, and it is found that the real frequency of the wave is not a sensitive function of κ, but the imaginary part of the frequency is. It is also shown that for those values of κ where a large number of resonant particles participate in wave–particle interaction, the wave is heavily damped, as expected. The possible application of the results to the solar wind is discussed.

关键词： magnetosonic wave suprathermal plasma wave-particle interactions damping of wave

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Evolutions of equatorial ring current ions during a magnetic storm

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Earth and Planetary Physics 2020年第2期4卷 131-137页

作者： Zheng Huang ZhiGang Yuan XiongDong Yu School of Electronic Information Wuhan University

In this paper, we present evolutions of the phase space density(PSD) spectra of ring current(RC) ions based on observations made by Van Allen Probe B during a geomagnetic storm on 23–24 August 2016. By analyzing PSD spectra ratios from the initial phase to the main phase of the storm, we find that during the main phase, RC ions with low magnetic moment μ values can penetrate deeper into the magnetosphere than can those with high μ values, and that the μ range of PSD enhancement meets the relationship: S(O^+) >S(He^+)>S(H^+). Based on simultaneously observed ULF waves, theoretical calculation suggests that the radial transport of RC ions into the deep inner magnetosphere is caused by drift-bounce resonance interactions, and the efficiency of these resonance interactions satisfies the relationship: η(O^+) > η(He^+) > η(H^+), leading to the differences in μ range of PSD enhancement for different RC ions. In the recovery phase,the observed decay rates for different RC ions meet the relationship: R(O^+) > R(He^+) > R(H^+), in accordance with previous theoretical calculations, i.e., the charge exchange lifetime of O^+ is shorter than those of H^+ and He^+.

关键词： ULF waves ring current wave-particle interactions radial transport geomagnetic storm decay rates

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Importance of electron distribution profiles to chorus wave driven evolution of Jovian radiation belt electrons

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Earth and Planetary Physics 2018年第5期2卷 371-383页

作者： Jing Huang XuDong Gu BinBin Ni Qiong Luo Song Fu Zheng Xiang WenXun Zhang Department of Space Physics School of Electronic Information Wuhan University Lunar and Planetary Science Laboratory Macao University of Science and Technology-Partner Laboratory of Key Laboratory of Lunar and Deep Space Exploration Chinese Academy of Sciences

wave-particle interactions triggered by whistler-mode chorus waves are an important contributor to the Jovian radiation belt electron dynamics. While the sensitivity of chorus-driven electron scattering to the ambient magnetospheric and wave parameters has been investigated, there is rather limited understanding regarding the extent to which the dynamic evolution of Jovian radiation belt electrons, under the impact of chorus wave scattering, depends on the electron distribution profiles. We adopt a group of reasonable initial conditions based upon the available observations and models for quantitative analyses. We find that inclusion of pitch angle variation in initial conditions can result in increased electron losses at lower pitch angles and substantially modify the pitch angle evolution profiles of > ~500 keV electrons, while variations of electron energy spectrum tend to modify the evolution primarily of 1 MeV and 5 MeV electrons. Our results explicitly demonstrate the importance to the radiation belt electron dynamics in the Jovian magnetosphere of the initial shape of the electron phase space density, and indicate the extent to which variations in electron energy spectrum and pitch angle distribution can contribute to the evolution of Jovian radiation belt electrons caused by chorus wave scattering.

关键词： Jovian radiation belt whistler-mode chorus wave-particle interactions electron distribution profile

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