The role of the background solar wind on solar energetic particle events.
Highly energetic particles traversing the near-Earth space environment pose a threat to satellites which our modern society depends on. In addition, future manned missions to the Moon and Mars will require protection against such radiation. Thus, a profound understanding of the particle radiation conditions in our solar system is crucial. Most of this radiation consists of electrons, protons, and heavier ions accelerated during solar eruptive events such as flares and coronal mass ejections (CMEs). The transport and acceleration of these solar energetic particles (SEPs) through the solar wind can be described by the focused transport equation (FTE).
In this thesis, we develop a numerical model that calculates energetic particle intensities in the inner heliosphere by solving the FTE under realistic solar wind conditions. This model is called PARADISE, an acronym for Particle Radiation Asset Directed at Interplanetary Space Exploration. PARADISE solves the FTE by integrating a set of Itô stochastic differential equations, while assuming a solar wind configuration obtained from a magnetohydrodynamic model; particularly, we use the EUHFORIA model. Using PARADISE, we investigate the transport of SEPs in a solar wind containing a corotating interaction region (CIR), and we show how such a CIR alters SEP distributions by acting as an efficient magnetic mirror and by re-accelerating particles in its associated compression and shock waves. Moreover, the intricate magnetic topology of the CIR can strongly affect the efficiency of cross-field diffusion in spreading particles through interplanetary space. Further, we study the effects of the magnetic field curvature and gradient drifts on the decay phase of SEP events. Even for low-energy protons (<36 MeV), drifts could inhibit the SEP flood phenomenon, unless they were mitgated by e.g., cross-field diffusion. Furthermore, particle drift effects are enhanced in non-nominal solar wind conditions, such as a CIR. Finally, we show the capability of PARADISE to model the evolution of SEP intensities in a dynamic solar wind containing a large-scale transient structure by injecting 100~keV protons in front of a CME.