A Global Kinetic Model For Electron Radiation Belt Formation And Evolution

The terrestrial radiation belt was discovered in 1958, and it has receiveda resurgence of interest in recent years. The main drivers are the fundamentalscience questions surrounding its complex and dramatic dynamics, and particularlyits potential hazards posed to space-borne systems. The establishment ofphysics-based radiation belt models will be able to differentiate the contributionsof various mechanisms, forecast the future radiation belt evolution, and then mitigateits adverse space weather effects. The test-particle and kinetic formulationsare two commonly used approaches for radiation belt model. This dissertationconcentrates on the construction and application of electron radiation belt kineticmodel, as well as the evaluation of the effect of various physical mechanisms.In the first chapter, we introduce the structure of inner magnetosphere, showthe electron radiation belt dynamics and its space weather effects, describe therelated basic theories, and propose the research contents of this dissertation.In the second chapter, we develop an electron radiation belt local diffusionmodel treating the cyclotron resonance of various plasma waves (chorus, hiss andelectromagnetic ion cyclotron waves). The numerical difficulty is how to fully solvethe local diffusion equations (including the pitch-angle, momentum and cross diffusionterms). We construct an efficient, stable and easily-programmed numericalscheme, named hybrid finite difference scheme, which is found to be able to overcomethe numerical instability when the cross terms are included. We detailedlyevaluate the roles of various cyclotron resonance in radiation belt dynamics, andthe effect of cross diffusion on the simulation results. Adopting a relatively realisticbackground density model, we quantify the influence of field-aligned densityvariation on the cyclotron resonance efficiency of chorus waves. We further generalizethe current local diffusion model, and present the first numerical simulation of plasmasheet electron phase space density evolution driven by chorus waves.In the third chapter, we develop a global electron radiation belt diffusionmodel STEERB treating the radial diffusion and cyclotron resonance. Numericaldifficulty still lies in the full solution of local resonant diffusion equation with crossterms. STEERB model is one of the first radiation belt models including crossterms, which is found to be efficient, stable and easily-parallelizable. We conductseveral idealized numerical simulations, reproduce the dominant characteristics ofelectron radiation belt during the quiet and geomagnetically active periods, andevaluate the contributions of radial diffusion and various cyclotron resonance tostorm-time electron radiation belt dynamics, as well as the influence of cross termson global simulation results.In the fourth chapter, we adopt a Dst-dependent background magnetic field,and self-consistently introduce the adiabatic transport into STEERB model. TheSTEERB model is the first global electron radiation belt diffusion model includingadiabatic transport. We perform several idealized simulations, and analyze thecontribution of adiabatic transport to electron radiation belt dynamics in thepresence or disappearance of other non-adiabatic processes. Using the data-drivenSTEERB model, we quantitatively simulate the electron radiation belt dropoutevent on 9 October 1990, and determine the dominant physical mechanisms inthis specific event. Over the past decades, significant progress has been made inthe theory and simulation for the enhancements of radiation belt electron fluxes,but relatively limited progress has been reported on the depletions. The currentwork improves our understanding on the electron radiation belt dropout process.In the fifth chapter, we further improve the STEERB model into a global electronradiation belt convection-diffusion model, treating the adiabatic transport,magnetospheric convection, radial diffusion and cyclotron resonance. The currentSTEERB model keeps efficient, stable and easily parallelizable, possesses hightemporal and spatial resolutions, and particularly has the capability of handlingsome transient process. Using the data-driven STEERB model, we quantitativelysimulate the 10 January 1997 substorm injection event, and analyze the contri- bution of substorm injection to electron radiation belt dynamics.In the sixth chapter, we review the developments of STEERB model and theobtained physical results, and finally propose the future improvements of STEERBmodel.