Propagation and Excitation of Electromagnetic Waves in the Earth's Inner Magnetosphere.

摘要

This dissertation addresses the generation and/or propagation of four plasma waves in the Earth's magnetosphere, electromagnetic ion cyclotron waves (EMIC), magnetosonic waves (MS), whistler-mode chorus, and plasmaspheric hiss. All four types of waves are important for dynamics of relativistic electrons in the Earth's radiation belts. The role of dayside and nightside chorus and EMIC waves in the storm time plume is evaluated by a pitch angle diffusion model of MeV electrons, where the effects of the distinct local time distributions of these waves are taken into account. We found that EMIC waves not only cause loss of MeV electrons, but also create gradients in the pitch angle distribution, which assists chorus waves in scattering MeV electrons into the loss cone. The ability of EMIC waves to cause scattering loss of relativistic electrons in models is sensitively dependent on the EMIC wave spectrum, especially the wave intensity just below He+ gyrofrequency. Later we carry out numerical simulation of the EMIC wave generation in a storm time magnetosphere, including a high-density plume with fine-scale density variation. Our simulation indicates that regions of preferential EMIC wave excitation are high density plumes and the plasmapause, and both the wave frequency spectrum and wave power are modulated by thermal plasma density variations inside the plume, which can reduce the electron minimum resonant energy down below 2 MeV. The effects of heavy ion composition on the minimum electron resonant energy are also evaluated. A new self-consistent physical model, obtained by coupling the Rice Convection Model (RCM), the Ring current and Atmospheric interaction Model (RAM), and ray tracing model (HOTRAY code), is used to simulate the transport and loss of ring current protons during the April 2001 storm and then calculate the path-integrated gain of EMIC waves globally throughout the storm. The resultant proton distribution is also analyzed for instability of magnetosonic waves, which is driven by harmonic cyclotron resonance with proton ring distributions, i.e., a peak in phase space density along the v⊥ axis. We find that the MS wave frequency spectrum is modulated by the ratio of ring velocity to the Alfvenic speed and MS waves with low harmonic proton gyrofrequencies ( 20OH+) tend to be unstable inside the high density plume and plasmasphere while MS waves with higher harmonic gyrofrequencies (> 20OH+) are unstable in the dayside trough region. In addition to the numerical simulation, proton rings are also observed from the MPA detector on board LANL spacecraft. These observed rings can be unstable to the MS waves over a broad range of local time from 1000 to 2200. Finally, we perform a ray tracing study on chorus waves in three dimensions, and find that chorus can evolve toward incoherent hiss due to multiple bounces inside the plasmapshere. Our 3D ray tracing study also accounts for the distinct local time distribution of those two emissions.