Solar Energetic Particle Acceleration and Transport at the Curved and Evolving Shock Driven by Coronal Mass Ejections

Abstract

Understating the spatial and temporal distributions of solar energetic particles (SEP) in interplanetary space is of particular interest from both scientific and space weather perspectives. In large SEP events, charged particles are accelerated by the collisionless shock waves driven by the coronal mass ejections (CMEs) continuously from the Sun to/beyond 1 AU that pose serious radiation hazards to astronauts and electronic equipment in space. In this thesis, we study the SEP acceleration and transport at CME-driven shocks with considering a number of factors regarding the properties of shock and solar wind, and quantitatively analyze their contributions to the spatial and temporal variations of SEP profiles. In Chapter 1, we give a brief introduction about the heliosphere, Rankine-Hugoniot conditions and the theory of diffusive shock acceleration. In Chapter 2, we develop a new kinematic model to simulate SEP acceleration at a spherical shock in the interplanetary magnetic field (IMF). This work shows that the evolution of shock geometry as the shock propagates outward from the Sun plays an crucial role in generating high-energy SEPs ($>10MeV$). Most of these particles are accelerated at west shock flanks near the Sun and transported to 1AU along the IMF where the acceleration rate is larger due to a quasi-perpendicular shock geometry. Also, the evolution of shock geometry will also produce many features in the energy spectra profiles, like bumps/dips and double power-law. In Chapter 3, we focus on the transport of SEPs in the IMF. We apply quasi-linear theory to compute the parallel transport diffusion coefficient ($\kappa_\parallel$) of SEPs based on the Parker solar Probe observations of magnetic field and solar wind plasma from 0.062 to 0.8 AU. We provide an empirical formula of $\kappa_\parallel$ as a function of heliocentric distance and particle energy that can be used as a reference in studying the transport and acceleration of SEPs as well as the modulation of cosmic rays in the IMF. In Chapter 4, we propose a data-driven, physics-based model to study the spatial variations of SEP profiles. The realistic setup of the model is based on data-driven magnetohydrodynamics simulations and coronagraphic observations of CMEs. With this model, we can explain the absence of high-energy SEPs in some very intense events and better understand many features in the time-intensity profiles of SEPs observed at 1AU. In Chapter 5, we summarize the main results of the dissertation and discuss potential future work in Chapter 6.