Parallel implementation of 3D global MHD simulations for Earth’s magnetosphere

AbstractThis paper presents a dynamic domain decomposition (D3) technique for implementing the parallelization of the piecewise parabolic method (PPM) for solving the ideal magnetohydrodynamics (MHD) equations. The key point of D3 is distributing the work dynamically among processes during the execution of the PPM algorithm. This parallel code utilizes D3 with a message passing interface (MPI) in order to permit efficient implementation on clusters of distributed memory machines and may also simultaneously exploit threading for multiprocessing shared address space architectures. 3D global MHD simulation results for the Earth’s magnetosphere on the massively parallel supercomputers Deepcomp 1800 and 6800 demonstrate the scalability and efficiency of our parallelization strategy

Influence of Photospheric Magnetic Conditions on the Catastrophic Behaviors of Flux Ropes in Solar Active Regions

Since only the magnetic conditions at the photosphere can be routinely observed in current observations, it is of great significance to determine the influences of photospheric magnetic conditions on solar eruptive activities. Previous studies about catastrophe indicated that the magnetic system consisting of a flux rope in a partially open bipolar field is subject to catastrophe, but not if the bipolar field is completely closed under the same specified photospheric conditions. In order to investigate the influence of the photospheric magnetic conditions on the catastrophic behavior of this system, we expand upon the 2.5-dimensional ideal magnetohydrodynamic model in Cartesian coordinates to simulate the evolution of the equilibrium states of the system under different photospheric flux distributions. Our simulation results reveal that a catastrophe occurs only when the photospheric flux is not concentrated too much toward the polarity inversion line and the source regions of the bipolar field are not too weak; otherwise no catastrophe occurs. As a result, under certain photospheric conditions, a catastrophe could take place in a completely closed configuration, whereas it ceases to exist in a partially open configuration. This indicates that whether the background field is completely closed or partially open is not the only necessary condition for the existence of catastrophe, and that the photospheric conditions also play a crucial role in the catastrophic behavior of the flux rope system

Eruption of Solar Magnetic Flux Ropes Caused by Flux Feeding

Large-scale solar eruptions are believed to have a magnetic flux rope as the core structure. However, it remains elusive as to how the flux rope builds up and what triggers its eruption. Recent observations found that a prominence erupted following multiple episodes of flux feeding. During each episode, a chromospheric fibril rose and merged with the prominence lying above. In this Letter, we carried out 2.5-dimensional magnetohydrodynamic (MHD) numerical simulations to investigate whether the flux-feeding mechanism can explain such an eruption. The simulations demonstrate that the discrete emergence of small flux ropes can initiate eruptions by feeding axial flux into the preexistent flux rope until its total axial flux reaches a critical value. The onset of the eruption is dominated by an ideal MHD process. Our simulation results corroborate that the flux feeding is a viable mechanism to cause the eruption of solar magnetic flux ropes

Numerical Simulations on the Deflection of Coronal Mass Ejections in the Interplanetary Space

Deflection of coronal mass ejections (CMEs) in the interplanetary space, especially in the ecliptic plane, serves as an important factor deciding whether CMEs arrive at the Earth. Observational studies have shown evidence for deflection, whose detailed dynamic processes, however, remain obscure. Here we developed a 2.5D ideal magnetohydrodynamic simulation to study the propagation of CMEs traveling with different speeds in the heliospheric equatorial plane. The simulation confirms the existence of the CME deflection in the interplanetary space, which is related to the difference between the CME speed (vr) and the solar wind speed (vsw): a CME will propagate radially as vr is close to vsw but eastward or westward when vr is larger or smaller than vsw; the greater the difference is, the larger the deflection angle will be. This result supports the model for CME deflection in the interplanetary space (DIPS) proposed by Wang et al., predicting that an isolated CME can be deflected due to the pileup of solar wind plasma ahead of or behind the CME. Furthermore, the deflection angles, which are derived by inputting vr and vsw from the simulation into the DIPS model, are found to be consistent with those in the simulation