Dynamic Evolution Of Low Frequency Waves And Energetic Particles In The Inner Magnetosphere

During geomagnetic storms, the fluxes of energetic particles in the inner-magnetospherechange drastically by several orders of magnitude over timescales ranging from hoursto days. These high energy particles can harm both spacecrafts and the navigationsystems. Hence, understanding the physical processes of the energetic particle fluxvariations have both scientific and practical significance. Wave-particle interactionsare considered to be the main mechanisms of the dynamic processes. There are manywaves with different frequencies and properties in the inner-magnetosphere, such aschorus waves, hiss waves and EMIC waves. Since the intensities and distributions ofthe waves can change drastically during the storm time, we need to understand theexcitation and propagation processes of the waves. When the waves resonate withthe particles in the periodic motions, the wave-particle interactions will be occurred,leading to the growth and damping of waves or the acceleration and loss of particles.The competition of those acceleration and loss process controls the dynamic evolutionin the inner-magnetosphere. In this study, we will focus on the EMIC wave excita-tions and the energetic electron evolutions driven by wave-particle interactions in theinner-magnetosphere.The EMIC waves can usually be categorized into two types by their observationalcharacteristics: board-band incoherent EMIC waves and rising tone coherent EMIC.Firstly, we report a board-band incoherent EMIC wave excitation event using RBSPsatellite data. On 10 October 2013, RBSP-B observed the geomagnetic indices, ～10ke V proton injection, the thermal proton anisotropy and the ambient magnetic fieldwhen the EMIC waves occurred. According to the linear theory, we suggest that theintense thermal proton injections and the decreasing magnetic field were responsiblefor the excitation of EMIC waves in this case. For the rising tone EMIC wave with highcoherent level, its frequency sweep rate strongly affects the efficiency of pitch-anglescattering. Based on the Cluster observations, we analyze three typical cases of risingtone EMIC waves. Two cases locate at the nightside(22.3 and 22.6MLT) equatorialregion and one case locates at the duskside(18MLT) higher magnetic latitude(λ =-9.3?) region. For the three cases, we derived the relative parameters from satelliteobservation, and input those data into the nonlinear wave growth model to simulatethe time-frequency evolutions of the rising tones. The simulated results show goodagreements with the observations of the rising tones, providing further support for theprevious finding that the rising tone EMIC wave is excited through the nonlinear wavegrowth process.The wave-particle interactions play an important role in the dynamic evolution ofthe radiation belt electrons. On 15 March 2013, RBSP-B detected the EMIC waveswith the energetic electron fluxes decreasing, and the low altitude NOAA satellitealso observed obvious high energy electron precipitations at the same L-shell andMLT region. We suggest that the cyclotron resonance between the waves and theenergetic electrons, leading to the precipitations of the electrons. The observationprovides a strong evidence for the theory of EMIC wave scattering energetic electrons.In addition, we report the multi-satellite(LANL, GOES-10 and Cluster) observationdata of electron flux evolutions and chorus wave excitation in the radiation belt duringthe geomagnetic storm and substorms from 10 to 14 January, 2002. The seed(50 –225 ke V) electron flux increased 50 times in five hours during the storm main phase,and the relativistic(>0.6 Me V) electron flux increased about 60 times at night sideduring the recovery phase. Meanwhile, the Cluster satellites detected intense choruswaves(the wave power up to ～10-3n T2Hz-1) at MLT≈3 when passing through theouter radiation belt. Using a Gaussian fit to the observed chorus spectra, we calculatethe drift-averaged diffusion coefficients and then solve a 2-D Fokker-Planck diffusionequation. We use the STEERB code to simulate the energetic electron flux evolutionsdriven by chorus waves in two cases: with and without seed electron injections. Theobtained results suggest that the injected seed electrons and chorus waves accelerationplay important roles in the buildup of the radiation belt electrons.The researches in our paper provide further support for the existing theories andenhances our understanding of the dynamic process in the inner magnetosphere.