Structure and dynamics of the inner magnetosphere and their effects on radiation belt electrons.

摘要

The goals of this dissertation are: (1) to understand the physics describing the structure and dynamics of magnetic field configurations in Earth's inner magnetosphere; (2) to assess the performance of data-based and physics-based global magnetospheric models under various conditions; and (3) to quantify the responses of global magnetic and electric fields to solar wind variations, and ultimately their effects on radial transport of radiation belt electrons. The radiation belt charged particle environment, the relativistic electrons in particular, changes by orders of magnitude on a variety of time scales in a complicated fashion. In order to understand and model the dynamic behavior of radiation belt electrons, we first need global, realistic, self-consistent, and time-dependent magnetospheric models. Therefore, we compare state-of-the-art empirical Tsyganenko models and Lyon-Fedder-Mobarry (LFM) physics-based code predictions with geosynchronous measurements to assess their performance and quantify the field configurations and fluctuations in the inner magnetosphere. The Tsyganenko storm model best predicts the large-scale field magnitude for all geomagnetic conditions, but fails to reproduce small-scale wave fields. On the other hand, the LFM code reproduces both the field configurations and ultra-low-frequency (ULF) waves during non-storm intervals. Next, we simulate the dynamics of radiation belt electrons using global magnetic and electric fields from the LFM code, driven by idealized solar wind over a range of velocities. We follow the trajectories of electrons, starting at different local times and radii for the same first adiabatic invariant, to understand their transport and energization through collective wave-particle interactions. Finally, we quantify the ULF wave effects on radiation belt electrons by calculating the radial diffusion coefficients from the LFM simulation results. The derived coefficients as a function of solar wind velocity, of 10-4 to 1 day-1 in the outer electron belt, are comparable to observational results after normalizing for wave power. Using this method, we conclude that diffusive electron transport is well simulated for various solar wind conditions and geomagnetic activity levels, a significant step toward quantitative understanding of the complex, dynamical radiation belt environment.