Study Of Ion Cyclotron Waves And Magnetosonic Waves In The Radiation Belt

Waves are important for electron flux evaluation in Radiation Belt.Hot ions in-jection during the substorms form the unstable ion distributions,which lead to the exci-tation of two low frequency waves.First is the Electromagnetic ion cyclotron(EMIC)waves,which is suggested to be account for the rapid loss of relativistic electrons dur-ing storms.Another is the Magnetosonic(MS)waves,which can Landau resonant with electrons near equator and accelerate electron to high energy or remove the 90° pitch angle electrons.We present study about these two waves.In the first chapter,we introduce the structure of radiation belt,basic dynamic pro-cesses and some waves,some relative background theories and models,the observation data and processing method,and provide the basic idea of this thesis.In the second chapter,we study the nonlinear scattering of high energy electron in oblique EMIC waves.Cyclotron resonant scattering by EMIC waves has been con-sidered to be responsible for the rapid loss of radiation belt high-energy electrons.The EMIC waves typically have large amplitudes of 1-10 nT,essentially violating the as-sumption of small wave amplitudes in the quasi-linear theory.For parallel-propagating EMIC waves,the nonlinear character of cyclotron resonance has been revealed in recent studies.Here we present the first study on the nonlinear fundamental and harmonic cy-clotron resonant scattering of radiation belt ultra-relativistic electrons by oblique EMIC waves on the basis of test-particle simulations.we find that:Both fundamental(l= 1)and harmonic(l =-1,2 and-2)cyclotron resonances can exhibit significant nonlin-earity for oblique EMIC waves.The nonlinear electron loss timescale is shorter than the quasi-linear prediction.As the wave normal angle increases,the differences between quasi-linear and test-particle transport coefficients tend to be reduced,the difference between quasi-linear and nonlinear loss timescales are also reduced.These results con-tribute to the development of the radiation belts' models by providing a more precise prediction for the resonant scattering of electrons by EMIC waves.In the third chapter,simultaneous observation of MS waves are performed.MS waves are the low-frequency whistler mode emissions,it can locally accelerate ener-getic electrons mirroring off the equator and produce the electron butterfly pitch angle distributions through the Landau resonance.Previous observations have shown that the MS emission lines can considerably deviate from the harmonics of the local proton gyro frequency.These discrepancies may be interpreted as a result of the MS wave prop-agation.However,it is challenging to directly validate this hypothesis because of the stringent requirements on satellite observations and data processing techniques.We per-form simultaneous observation of MS waves using the high-resolution frequency-time characteristic data of Van Allen Probes.We find that:At higher L shells,the substorm-injected hot protons excited the discrete magnetosonic emissions which exhibited a clear rising tone characteristic in the frequency-time spectrograms.At lower L shells free from substorm injection of hot protons,the magnetosonic emissions emerged nearly at the same time as those at higher L shells and possessed the consistent frequency-time characteristics.These results support the prediction of proton Bernstein mode insta-bility theory and the hypothesis about wave propagation.These help to improve the models of magnetosonic waves and make possible of a more precise simulation for the interaction between electrons and magnetosonic wavesIn the forth chapter,we conclude the work about EMIC scattering of electrons and the propagation of magnetosonic waves.We also propose future works about these waves.