Scattering Effects Of Electromagnetic Ion Cyclotron Waves On Magnetospheric Particles

Electromagnetic ion cyclotron(EMIC)waves have received increasing attention in recent years,mainly due to their role in the scattering loss of magnetospheric particles.Via cyclotron-resonant interactions,EMIC waves can result in the rapid precipitation loss of radiation belt electrons into the atmosphere and significantly affect the Earth's radiation belt dynamics.Due to the potential hazards of energetic electron posed to space-borne systems,EMIC waves may mitigate the adverse space weather effects caused by these electrons.On the other hand,EMIC waves can cause the scattering loss of ring current protons,thereby contributing to the decay of the terrestrial ring current.Subsequently,the precipitation of energetic protons into the atmosphere can contribute to the formation of detached subauroral proton arcs.This dissertation focuses on the resonant interactions between EMIC waves and various magnetospheric particles,as well as the role of EMIC waves in the dynamic evolution of these particles.In the first chapter,we introduce the basic structure of the Earth's magnetosphere and the motion of charged particles in the magnetic field,describe three basic mechanisms of the resonant wave-particle interactions,i.e.,cyclotron resonance,bounce resonance and drift resonance,and show the spectral properties,generation mechanism,and global distribution of EMIC waves.In the second chapter,we briefly introduce the general dispersion relation of plasma waves and show the deviation of cold and hot plasma dispersion relations of EMIC waves.In the third chapter,based on the cold plasma dispersion relation of EMIC waves,we extend the determination of the resonant frequency roots to a cold,multi-ion(H+,He+ and O+)plasma and subsequently quantify the cyclotron-resonant scattering loss of radiation belt electrons,ring current protons and central plasma sheet protons by EMIC waves.We first report the simultaneous presence of three emission bands(H+,He+ and O+)in an EMIC wave event.By quantifying the respective and combined scattering effects of electrons by three EMIC bands,we find that He+ band dominates this scattering process.Then we investigate the influence of EMIC wave normal distribution on the pitch-angle diffusion of both radiation belt electrons and ring current protons and find that the increase of wave normal obliquity can obviously reduce the efficiency of EMIC wave-induced pitch-angle scattering.Finally,by investigating the scattering properties of central plasma sheet protons by EMIC waves,we demonstrate that EMIC waves should be responsible for the 'reversed' energy-latitude dispersion pattern of proton precipitation.In the fourth chapter,we investigate the bounce-resonant interactions between H+ band EMIC waves and radiation belt electrons,and analysis the sensitivity of bounce resonance region to the resonance order.By calculating the bounce resonance diffusion coefficients,we demonstrate that bounce resonant interactions between EMIC waves can efficiently scatter near-equatorially mirroring electrons to lower equatorial pitch-angles,and subsequently precipitate these electrons into the atmosphere under the impact of other cyclotron resonance mechanisms.For the first time,we prove that,in addition to EMIC waves,low-frequency plasmaspheric hiss can also bounce-resonate efficiently with radiation belt electrons.Quantitative calculations show that bounce-resonate pitch-angle diffusion coefficients by both low-frequency hiss and EMIC waves are strongly dependent on electron equatorial pitch-angle.Compared with EMIC waves,hiss with higher frequencies can bounce-resonate with higher resonance orders and therefore resonate with electrons with broader resonance region.In the fifth chapter,we study the hot plasma effects on the scattering loss of radiation belt electrons by EMIC waves.EMIC wave-driven loss of electrons is mainly controlled by two factors,i.e.,electron minimum resonant energy and bounce-averaged pitch-angle diffusion coefficients.While minimum resonant energy determines the minimum energy of electrons that can be scattered by EMIC waves,pitch-angle diffusion coefficients indicate the corresponding scattering efficiency.Using the hot plasma dispersion relation of EMIC waves,we find that in a realistic plasma environment,EMIC waves can only cause significant loss of ultra-relativistic(>2MeV)electron fluxes,thereby providing a theoretical explanation for the discrepancy between previous theoretical studies and recent observations.We further investigate the hot plasma effects on the electron pitch-angle diffusion coefficients.It is proved that inclusion of hot protons will obviously modify the results of pitch-angle diffusion coefficients and this modification is strongly dependent on the electron energy and equatorial pitch-angle.We thus demonstrate the significance of including hot plasma effects in the EMIC wave-driven electron loss and improve the current understanding of radiation belt electron dynamics.In the sixth chapter,we review the obtained results about EMIC waves,and finally propose the future investigations.