Magnetic Field Overlying Solar Eruption Regions and Kink and Torus Instabilities

Using a Potential Field Source Surface model (PFSS), we study magnetic field overlying erupted filaments in solar active regions. The filaments studied here were reported to experience a kink instability or a torus instability. The torus instability leads to a full eruption, while the kink instability leads to a full eruption or a failed eruption. It is found that for full eruption the field decreases with height more quickly than that for failed eruption. A dividing line between full eruption and failed eruption is also found to be likely connected with the decay index n of the horizontal potential field due to sources external of the filament ( n = −d log(Bex)/d log(h), where h is height): the decay index of failed eruption tends to be smaller than that of full eruption. The difference of the decay indexes between full eruption and failed eruption is statistically significant. These are supportive of previous theoretical and numerical simulation results. Another significant difference is the field strength at low altitude: for failed eruption, the field strength is about a factor of 3 stronger than that for the full eruption. It suggests that the field strength at low altitude may be another factor in deciding whether or not a full eruption can take place. On the other hand, the decay index for the torus-instability full eruption events exhibits no trend to exceed the decay index for the kink-instability full eruption events on average, different from a suggestion derived from some MHD simulations. We discuss possible reasons that may cause this discrepancy. Subject headings: Sun: activity; Sun: coronal mass ejections (CMEs); Sun: magnetic fields