Observations And Excitation Of Plasma Waves In The Inner Terrestrial Magnetosphere

It is well known that most of the solar-terrestrial space is full of plasma.One of the most common and inherent physical phenomenon is the plasma waves,which can play an important role in energy and material transformation inside the solar-terrestrial system.One one hand,plasma waves are essentially energy carriers.As these waves shuttle forth and back,energy carried in them can achieve cross-region transformation.On the other hand,plasma waves are able to be amplified by absorbing energy from particles in plasma.In constrast,plasma waves can transfer their energy to particles in terrestrial magnetosphere,leading to particle acceleration and energization.When energy reaches to rather high level,particles may cause irreparable damage to spacecrafts.Additionally,plasma waves can result in precipitation of particles in the terrestrial magnetosphere into the atmosphere through pitch angle scattering,which has been demonstrated to be one potential generation mechanism of aurora.The most common waves in the terrestrial magnetosphere consist of electromagnetic ion cyclotron(EMIC)waves,fast magnetosonic(MS)waves,whistler-mode waves(including hiss waves,chorus waves,banded whistler waves and so on),etc.How do these waves distribute in the magnetosphere?How can these waves be excited,and what is the dominant factors during their excitation?After excitation,what effects would these waves make on particles?Since recent satellite missions are lauched with more advanced and sophisticated instruments,had some new properties of any known waves been observed?had any predicted wave modes in theoretically,or even unknown wave modes,been found?Can these new characteristics or/and wave modes be understood through existing theoretical results,or some new mechanisms are needed?These questions are what the space and laboratory plasma scientist want to answer.In this thesis,based on the Van Allen Probes,and Magnetospheric Multiscale mission observations and kinetic theory,we study these basic physical processes,and the results are mainly shown in the following.1.Spatial distribution properties of O+ band EMIC waves in the magnetosphere are reported via "Van Allen Probes data.Since these O+ band EMIC waves are observed to have properties different from previous EMIC waves,we have proposed a new excitation mechanism,based on ring distributions,to exposit the free energy source for these O+ band EMIC waves.This excitation mechanism has also been verified through satellite in situ observations.In the meanwhile,we have found that the density of background plasma and the oxygen ion composition in the background plasma can play an important role in the excitation of O+ band EMIC waves.2.Based on the Magnetospheric Multiscale mission observations,several typical cases and the spatial distribution of He2+ band EMIC wave events are reported.Through analysis of particle data,generation mechanism of these waves are proposed,Additionally,we have presented a typical case of EMIC waves with vanishing He+ stop band.Results from in situ ion observations and kinetic theory verify that cold He+ heating caused by EMIC waves can make the usual He+ stop band vanished.3.A unique case of modulation of MS waves by background plasma density are reported for the first time.In the case,as the Van Allen Probe A moves cross dense and teneous plasma alternatively,enhanced MS waves are observed only in teneous plasma regions.Using linear growth theory,we have verified that background plasma can modulate the MS wave intensity by controlling their linear growth rate.Meanwhile,in low density regions,MS waves can not only grow more easily,but also heat cold particles in the plasmasphere,through which energy stored in ring current ions can be transferred into plasmaspheric particles.4.Through observations of the Van Allen Probe mission,low-frequency chorus waves are reported.Comparison between theoretical calculation and observations verify that these low-frequency chorus waves prefer to occur in high density regions.On the other hand,we fistly report that the frequencies of banded whistler waves would shift upward during solar wind dynamic pressure enhancement,which has been verified to be resulted from the enhanced temperature anisotropy of electrons caused by enhanced solar wind dynamic pressure.