Influence of photospheric magnetic flux distribution on coronal flux rope catastrophe

Previous studies of coronal magnetic flux rope systems indicated that these systems exhibit a catastrophic behavior for background fields with a specific photospheric flux distribution, and that the catastrophic energy threshold exceeds the associated open field energy. In this Letter, we take axisymmetrical bipolar fields in spherical geometry with different flux distributions on the photosphere as the background, and then examine how the flux distribution affects the catastrophic behavior and the energy threshold of a flux rope system. It is found that when the photospheric flux is concentrated too much toward the equator, the flux rope system loses its catastrophic behavior, i.e., that it evolves smoothly with the change of the rope properties. On the other hand, if the flux shifts poleward more than a split monopole field, a catastrophe behavior is recovered, and the catastrophic energy threshold increases in magnitude and percentage relative to the associated open field energy with increasing poleward shift of the flux. As a result, the flux rope erupts upward after catastrophe with a faster acceleration and a larger final speed when the flux is concentrated more toward the solar poles.