Observations And Simulations Of Unusual Whistler Waves In The Radiation Belts

The terrestrial radiation belts are regions of inner magnetosphere that are popu-lated by charged particles with energies>100 keV.The radiation belt electrons have been found to exhibit dramatic dynamics and pose serious hazards to space-borne sys-tems and astronauts.It is commonly believed that the complex dynamics of radiation belt electrons are caused by the competition and cooperation of various acceleration,loss and transport mechanisms.In particular,the cyclotron resonance by whistler-mode waves is considered an important acceleration and/or loss mechanism for radiation belt electrons.In this thesis,on the basis of Van Allen Probes observations,we investi-gate the evolution of some unusual whistler-mode waves and their potential effect on radiation belt electrons.In the first chapter,we introduce evolutions of the radiation belts,describe contri-butions of wave-particle interactions,and propose the research contents of this thesis.In the second chapter,we introduce the Van Allen Probes instruments and data analysis methods,and show some examples of different plasma waves in the radiation belts.In the third chapter,we concentrate on intense low-frequency chorus waves.Cho-rus waves are usually considered to occur in the frequency range 0.1-0.8fce.The ob-servations of Van Allen Probes show that intense chorus waves can occur even below 0.1 fce.These emissions are found to propagate quasi-parallel to the magnetic field and exhibit hiss-like signatures most of the time.The low-frequency chorus can produce rapid loss of seed(～0.1 MeV)electrons,different from the normal chorus.For high-energy(≥0.5 MeV)electrons,the low-frequency chorus can yield comparable momen-tum diffusion to that of the normal chorus but much stronger pitch angle ’diffusion near the loss cone.The results suggest that the intense low-frequency chorus potentially plays a different role from normal chorus,which should be included in the radiation belt models.In the fourth chapter,we concentrate on the chorus emissions with long-lived os-cillating tones.Chorus emissions typically appear as a hiss-like band and/or a series of short-lived(up to～1 s)discrete elements.The observations of Van Allen Probes demonstrate that chorus can possess long-lived(up to 25 s)oscillating tones.These highly coherent oscillating tones are found to be generated naturally rather than being related to some artificial signals.Possible scenarios for the generation of the oscillat-ing tone chorus are as follows:(1)being nonlinearly triggered by the accompanying hiss-like bands,or(2)being caused by the modulation of the wave source.The details of the generation and evolution of such a long-lived oscillating tone chorus need to be investigated in the future.In the fifth chapter,we concentrate on the amplification process of exohiss.Ex-ohiss is commonly considered the plasmaspheric hiss leaked out of the plasmapause,potentially contributing to the loss of radiation belt electrons outside the plasmasphere.However,the evolution of exohiss after the leakage has not been fully understood.The observations of Van Allen Probes indicate that substorm-injected energetic electrons with energies～100 keV can effectively amplify exohiss waves.This study reveals an important step,local amplification,of the exohiss evolution outside the plasmasphere.In the sixth chapter,we summarize the obtained results,and propose future works about these unusual whistler-mode waves.