| As an important plasma wave mode in the terrestrial magnetosphere,electromagnetic ion cyclotron wave(EMIC wave)can cause the rapid precipitation of charged particles to the atmosphere and their subsequent losses because of collisions with atmospheric molecules,which can significantly influence the dynamic evolution of magnetospheric particles.In terms of the processes of resonant wave-particle interactions,EMIC waves can drive efficient scattering of radiation belt relativistic electrons for atmospheric loss,result in rapid depletion of ring current protons during geomagnetic storms,and also lead to reversed energy-latitude dispersion pattern of central plasma sheet proton precipitations.This dissertation focuses on comprehensive investigation of the spatial distribution features and generation mechanism of EMIC waves and their scattering effects on magnetospheric electrons.Firstly,by using the recent Van Allen Probes data,we perform a statistical analysis to study the global distributions of H+-band,He+-band,and simultaneous H+-and He+-band EVMIC waves,respectively.Secondly,based on the kinetical linear theory,we study in detail the excitation processes of H+-band,He+-band,and O+-band EMIC waves under the ambient thermal plasma environment and the dependence of the linear growth rate of EMIC waves on the ambient plasma parameters.Thirdly,we perform a parametric study on the bounce resonant interactions between EMIC waves and magnetospheric electrons and the resultant electron scattering rates that can modulate the dynamic evolution of magnetospheric electrons.The principal results of this dissertation are summarized as follows:1.Based on the data from Electric and Magnetic Field Instrument Suite and Integrated Science(EMFISIS)instrument onboard Van Allen Probes during the period from 8 September 2012 to 31 December 2017,we identify 1009 H+-band events,1565 He+-band events,and 182 simultaneous H+-and He+-band events of EMIC waves,and investigat the global distributions of average wave amplitude and occurrence rate of these events.Our results demonstrate that EMIC waves with smaller amplitudes can be easier to excite and EMIC waves with larger amplitudes can have a longer duration.As the AE*index(the average value of AE index in the previous hour)increases,the occurrence rate of ENMIC wave events on the dayside increases.When the solar wind dynamic pressure or the geomagnetic activity level increases,the number of EMIC wave events significantly decreases,which can be mainly attributed to the infrequent occurrence of such extreme space weather conditions.H+-band EMIC waves occur primarily on the duskside at L = 4-6,while He'-band EMIC waves have a higher occurrence rate than H+-band,and exist widely in the inner magnetosphere at L = 2.5-6.For the simultaneous H+-and He+-band EMIC wave events,the amplitudes of He?-band EMIC waves dominate over H+-band at L = 3-6.With the increase of AE*index,the amplitudes of He'-band EMIC waves also increased more rapidly than H+-band.2.Based on the kinetic linear theory,we perform a parametric analysis on the linear growth of EMIC waves under the ambient thermal plasma environment and its dependence on the relative concentrations of multiple cold ions and density,temperature and temperature anisotropy of hot ions.Our results demonstrate that inclusion of hot ions can not only significantly contribute to the generation/growth of EMIC waves,but also largely alter the real part of EMIC wave hot plasma dispersion relation.Under certain space plasma environment,EMIC waves can be even excited in the stop band that occurs in the cold plasma regime.Increase of hot proton density can provide more free energy for EMIC wave excitation and thus enhance the occurrence possibility of H+-and He'-band EMIC waves in the magnetosphere.While the generation of H+-band EMIC waves requires higher temperature anisotropy of ring current protons,the linear growth of He+-band EMIC waves strongly depends on the temperature of ring current protons and the ambient plasma density.Increase of cold heavy ion abundance can facilitate the linear growth of 0+-band EMIC waves but inhibit the generation of H1-band EMIC waves due to increased damping.In addition,inclusion of hot He+ and 0+ions can result in stronger damping of H+-band and He+=band EMIC waves,respectively,thereby inhibiting the wave excitation and growth.Such an inhibition effect becomes more apparent with the increase of the thermal ion concentration,temperataure and temperature anisotropy.3.We perform a parametric investigation on the bounce resonant interactions between EMIC waves and magnetospheric electrons.Our results demonstrate that H+-and He+-band EMIC waves can efficiently pitch angle scatter magnetospheric electrons through the bounce resonance processes,which can result in the diffusive transport of near 90° pitch angles electrons to lower pitch angles.The bounce resonant scattering effects show a strong dependence on L-shell,electron kinetic energy and pitch angle.For magnetospheric electrons,bounce resonance by H+-band EMIC waves can occur over a broad range of L-shell.As the L-shell increases,the harmonic order of bounce resonance becomes smaller,and the net bounce resonant contribution decreases.The bounce resonance scattering rates also increase with increasing equatorial pitch angle.With the increase of the harmonic order,EMIC waves can bounce-resonate with lower energy electrons.The features of bounce resonant scattering effects of He'-band EMIC waves are overall similar to those of H+-band,including their dependence on L-shell,pitch angle and electron energy,while there are less bounce resonant harmonics for He+-band EMIC waves along with a smaller range of resonant electron energy.Our results indicate that while that cyclotron resonance with EMIC waves acts as an efficient depletion mechanism of radiation belt relativistic electrons,bounce resonance with EMIC waves provides another viable loss candidate for middle-to-low energy electrons in the Earth's radiation belts and ring current. |
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