CMEs and Interplanetary Shocks: 2.5D Numerical Modeling

Solar flares, eruptive prominences (EPs), and coronal mass ejections (CMEs) significantly impact Earth's environment and human habitability, as they are different manifestations of solar storms. Sometimes, solar energetic particle events (SEPs) are associated with interplanetary shocks driven by CMEs that propagate through the turbulent solar wind. We investigate the physical mechanisms of these phenomena in a more realistic gravitationally stratified solar atmosphere using 2.5D magnetohydrodynamics (MHD) and particle simulations. Our research covers three main topics:

(1) MHD simulations of solar flux rope eruptions and prominence formation: Starting from the standard solar eruption model, we employed 2.5D MHD simulations to investigate two scenarios of flux rope and prominence eruptions within a more realistic, gravitationally stratified solar atmosphere. We developed an enhanced levitation model for prominence formation and proposed a novel mechanism involving plasmoid-fed processes in the current sheet. The former is driven by photospheric converging motions, while the latter focuses on the catastrophe model of flux rope eruption and emphasizes the crucial role of magnetic reconnection in prominence formation. These models describe the formation of flux ropes during eruption and pre-existing flux ropes beforehand, respectively. Additionally, we explored "mesoscale" phenomena during flux rope eruption and their association with Quasi-Periodic Pulsations (QPPs), reproducing multi-wavelength observational images.

(2) Shock-turbulence interactions in interplanetary space: Solar wind turbulence is ubiquitous, and when CMEs propagate through the solar wind, they drive interplanetary shocks that interact with solar wind turbulence, which is one of the sources of SEPs. These interactions result in a turbulent downstream fluid. We found that after shocks propagate across turbulence, the downstream occurrence of plasmoids (i.e., small magnetic flux ropes in the solar wind) increases, saturates to a peak value for a certain interval, and then gradually decreases away from the shock. This behavior is consistent with in-situ measurements taken by the Magnetospheric Multiscale (MMS) mission at Earth's bow shocks. These plasmoid structures are important for plasma heating and particle acceleration.

(3) Particle accelerations during solar eruptions: We investigated particle acceleration during solar eruptions, focusing on: 1) test-particle modeling of non-adiabatic motion of particles in 2D magnetic islands and 2) a combined Particle-In-Cell (PIC) and MHD approach (PIC-MHD) to study particle acceleration at interplanetary shocks. In the PIC-MHD approach, the background thermal plasma is treated as a magnetofluid, while the motion of non-thermal particles is influenced by the Lorentz force. This method accounts for electromagnetic interactions between non-thermal particles and the background magnetofluid, potentially leading to upstream self-excited turbulence that enhances particle acceleration through various mechanisms.

Overall, our research focuses on various processes in solar storms. Understanding and even predicting these phenomena are crucial for studying their impact on human habitability.