Numerical modeling of drift resonance and drift-bounce resonance between ultra-low frequency waves and energetic particles in the inner magnetosphere

  • Author / Creator
    Wang, Chengrui
  • The main topic of this thesis is the investigation of drift resonance and drift-bounce resonance between energetic particles and Pc3-5 Alfvenic ultra-low frequency (ULF) waves in the Earth's inner magnetosphere. We have developed numerical models to simulate how the dynamics of O+, H+ ions and electrons are affected by Alfven waves in a dipole magnetic field. These models are used to interpret observations on differential particle flux variations that are caused by interactions with ULF waves in the magnetosphere. Observational data from different satellite projects, such as Cluster and Van Allen Probes, and from the CARISMA ground magnetometer observatory array are introduced to investigate the characteristics of ULF waves and the corresponding energetic particle flux variations.

    We present observational studies on two fast-damped ULF wave events observed by Cluster after an interplanetary shock. Comparisons between multi-satellite observations suggest that Landau damping is more effective in the plasmasphere boundary layer than in the plasmasphere due to the relatively higher proportion of Landau resonant ions that exist in the plasmasphere boundary layer. Also, the energy exchange between waves and particles through Landau damping is considered to be more efficient when heavier ions such as O+ are present. Based on the analysis of these events, further studies with computation models are recommended for wave-particle interactions.

    The test-particle simulations presented in this thesis reproduced several features of the pitch angle and energy spectrum of ion differential fluxes observed by the Van Allen Probes-A spacecraft on October 6, 2012. The observed and simulated fluxes are well correlated with giant pulsations of frequency f~10mHz and contain modulations in a narrow range of energy, with stronger enhancements occurring for non-equatorially mirroring particles. For ions at 35 pitch angle, a maximum in the differential flux oscillations occurs at an energy of 150keV, which is consistent with predictions made with drift resonance theory. The lack of enhanced differential fluxes of particles near the 90 pitch angle can be explained by the dependence of the resonance energy on the pitch angle.

    The electron flux modulations in ULF waves observed by RBSP-A on October 31, 2012 have been reproduced with our simulation results. The simulated fluxes have larger amplitudes and slower attenuation rates than observed fluxes due to the finite energy resolution of the MagEIS instrument on the spacecraft. When they are binned in energy as in the MagEIS instrument, they appear remarkably similar to the observed fluxes. Test particle simulations of N=0 drift resonance and N=-2 drift-bounce resonance with O+ ions reveal complex dynamics in which different wave-particle resonances can potentially interact. These simulations illustrate the expected behavior of ring current energetic ion populations in a region where poloidal mode ULF waves are ubiquitous.

    Another MHD Alfven wave model with a more realistic ionosphere boundary condition has been used to study the drift-bounce resonance of H+ ions with second harmonic ULF field line resonance. We used the forward Liouville method and the Monte Carlo method to reconstruct the distribution function of H+ ions when they interacted with ULF waves. It has been demonstrated that second-harmonic poloidal mode waves are efficient in energizing ions to tens of keV over timescales of tens of minutes. The test-particle simulations of bounce-resonance reproduce particle signatures which agree with theoretical predictions.

  • Subjects / Keywords
  • Graduation date
    Fall 2018
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
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