Electromagnetic Ion Cyclotron (EMIC) Waves In The Inner Magnetosphere And Its Resonant Interactions With Radiation Belt Relativistic Electrons

After its discovery in1958by Dr. Van Allen on basis of the measurements of Explore1, the Earth’s radiation belts attract extensive attention for intensive investigations, since this donut-lie region heavily occupies high-energy electrons and ions, which can have the velocities comparable to or approaching the light speed and pose a potentially significant hazard to both satellites and astronauts in space. The radiation belt electrons with extremely high energies, i.e.,>1MeV, are also called ’killer electrons’. The ’killer electron’ fluxes show dynamic variations with respect to different geomagnetic conditions. In order to forecast the environment in the radiation belt, the reasons for the change of the fluxes of the ’killer electrons’ become significant. Since the decrease of the relativistic electrons could reduce the hazards to satellites and humans in space, this dissertation focuses on the decrease mechanism of the relativistic electrons. It is considered that there are three factors reducing the flux of high energy particles in the radiation belt:the so-called ’magnetopause shadowing’, adiabatic outward transport, and wave-particle interactions caused precipitation. Because the wave-particle interactions caused precipitation of the relativistic electrons would affect the ionosphere and atmosphere of our Earth, further affect the living environment of our human beings, our research focus on the wave-particle interaction caused precipitation of relativistic electrons. During the various waves which can interact with relativistic electrons and then drive them precipitating, EMIC waves are the most efficient waves that can drive the precipitation rapidly. Therefore, in this thesis, the wave-particle interaction between the relativistic electrons in the radiation belt and electronic magnetic ion cyclotron waves (EMIC waves) are investigated.Based on the scientific goal presented above, our main researches and results are summarized as follows:(1) Study about the wave-particle interaction between relativistic electrons and EMIC waves which are caused by the compression of the magnetosphere. With coordinated observations of the NOAA15satellite and OUL magnetometer station in Finland, we report that the electromagnetic ion cyclotron (EMIC) waves which were stimulated by the compression of the magnetosphere drive relativistic electrons precipitation in geoquiescence on1Jan2007. After an enhancement of solar wind dynamic pressure (SWDP), a dayside Pcl pulsation was observed by the OUL station. Such a Pcl pulsation is caused by an EMIC wave which propagates from the generation place to lower altitudes. Simultaneously, the NOAA15satellite registered an enhancement of precipitating electrons count rates with energies>3MeV within the anisotropic zone of proton. This phenomenon is coincident with the quasi-linear theoretical calculation presented in this paper. Our observations suggest that after a positive impulse of solar wind, the compression-related EMIC waves can drive relativistic electrons precipitation and play a pivotal role in the dynamic of radiation belts. When the geomagnetic conditions are quiet, the effect of solar wind dynamic pressure to the earth is researched. It is proved that the enhancement of the solar wind dynamic pressure can decrease the flux of relativistic electrons in the outer radiation belt by the associated EMIC waves which can drive the precipitation of high-energy electrons. Therefore, compression related EMIC waves play important role in the evolution of the radiation belt.(2) Investigate about the occurrence rate and distribution characteristic of EMIC waves in the inner magnetosphere. Utilizing the data of Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) instrument onboard the Van Allen Probe A from Sep2012to April2014, during which period the apogee of the satellite has precessed all the MLT sectors, we obtain the statistical distribution characteristic of EMIC waves in the inner magnetosphere at all local times from L=3to L=6.5. Compared with the previous statistical results about EMIC waves, due to the lower orbit of Van Allen Probe, some new results are obtained. The important discoveries are summarized as follows:First important results are about the distribution characteristic of EMIC waves. The EMIC waves distribute relatively uniform in the MLT sectors in lower L-shells. On the other hand, there are indeed some peaks of the occurrence rate for the EMIC waves, especially in the noon, dusk and night sectors in higher L-shells. In the dawn sector, EMIC waves appear at lower L-shells comparing with those in other sectors. In the region with lower L-shell value (L<4), the occurrence rate of EMIC waves in the dawn sector is significant, and in some region even dominates during the occurrence rates in the four sectors. In contrast, in the regions with higher L-shell values (L>4) the occurrence rates of EMIC waves in the dusk sector are the most significant. This result implies the important role of the plasmapause or plasmaspheric plume:in lower L shells, the magnetosphere distribute uniformly, while in higher L shells, the plasmapause or plasmaspheric plume extend to higher L shells in the dusk sector.Second new discoveries are about the different distribution characteristics of hydrogen and helium EMIC waves. We investigated the characteristics of the hydrogen band EMIC waves and the helium band EMIC waves. Surprisingly, in the inner magnetosphere, hydrogen band EMIC waves occur more frequently than the helium band EMIC waves, which is converse in other previous studies. Additionally, they both have peaks of occurrence rate in noon, dusk and night sectors, among which the hydrogen band EMIC waves have more obvious peaks in the night sector than the helium band EMIC waves do, while the helium band EMIC waves are more concentrated in the dusk sector than the hydrogen band EMIC waves.Third results imply the significant role solar wind pressure plays in the generation of EMIC waves. Both of the hydrogen and helium EMIC waves occur frequently in the noon sector, which demonstrate the important role of the solar wind dynamic pressure.