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

Abstract

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

“…Our simulations demonstrate flux feeding as a viable mechanism to prepare a flux rope for the upward catastrophe in the physical space, not just in the parameter space. It is noteworthy that, because of the different initial states and simulating procedures, the critical axial fluxes in, e.g., Zhang et al (2017a), are not exactly the same as ours, and the rope systems eventually reach equilibria in that study.…”

“…In our simulations, we change C E to investigate the influences of different flux feeding processes on the major flux rope system. It should be noted that the science focus and simulating procedures in this work are quite different from those of Zhang et al (2017a), in which the catastrophic behaviors of a single flux rope was investigated.…”

“…For example, it was found that there exists a critical value of the total axial (also called toroidal in a Tokamak configuration) magnetic flux of a flux rope (e.g. Bobra et al 2008;Su et al 2009Su et al , 2011Zhang et al 2016Zhang et al , 2017aZhuang et al 2018). If the axial flux of the rope is smaller than this critical value, the rope system stays in equilibrium states; when this critical value is exceeded, loss of equilibrium occurs in the rope system: the flux rope jumps upward, with magnetic reconnection occurring below it, so that the rope erupts outward.…”

How flux feeding causes eruptions of solar magnetic flux ropes with the hyperbolic flux tube configuration?

“…Here we select a partially open bipolar field as the background field, in which a negative and a positive surface magnetic charge located at the photosphere within −b < x < −a and a < x < b, respectively. The background field could then be obtained by the complex variable method (e.g., Hu et al 1995;Zhang et al 2017). The background magnetic field can be cast in the complex variable form…”

Coronal Flux Rope Catastrophe Associated With Internal Energy Release

“…The catastrophic model of coronal magnetic flux rope is a very promising scenario to serve as a possible mechanism for triggering these eruptions (e.g., Hu & Wang, ; Lin et al, ). The catastrophe, belonging to nonlinear instability (Golubitsky, ; Saunders, ), requires a sudden transition of a flux rope system evolving from a quasi steady state into a dynamic state and is found to exist under certain conditions (e.g., Chen et al, ; Forbes & Isenberg, ; Forbes & Priest, ; Guo & Wu, ; Hu, ; Hu et al, ; Isenberg et al, ; Lin et al, ; Sun & Hu, ; Zhang et al, ). Within the catastrophe scenario, the magnetic energy which is stored in the corona is suddenly released (Chen et al, ; Zhang et al, ), and then results in a destabilization of the global magnetic field topology and an upward eruption of the flux rope.…”