Magnetic Flux Rope Eruption: Non Equilibrium versus Torus Instability
Abstract
The coronal magnetic configuration of an active region typically evolves quietly during few days before becoming suddenly eruptive and launching a CME. The precise origin of the eruption is still debated. Among other mechanisms, it has been long proposed that a loss of equilibrium, or an ideal MHD instability such as the torus instability, could be responsible for the sudden eruptivity. We first revisit both approaches with simple analytical models as well as with a 3D MHD simulation of an initially potential bipolar field, which evolves by means of simultaneous slow magnetic field diffusion and shearing motions in the photosphere. Reconnection of sheared arcade leads to the formation of a twisted flux rope, which corresponds to an electric current channel. We find that the electric current distribution and the field-line organization present in the MHD simulation provide an explanation for the recent X-rays Hinode observations of erupting sigmoidal regions. Next, we show analytically that the loss of equilibrium and the torus instability are two different views of the same physical mechanism. We compare the instability thresholds in the limit of straight and circular current channels, finding that they are closely comparable for thick current channels (as present in the MHD simulation and as expected in the corona) while these thresholds are well distinct at the limit of very thin current channels (as typically found in previous studies). Finally, including photospheric line tying of the current channel in the analytical models permits to have a closer comparison between instability thresholds found analytically and by the MHD simulation.
- Publication:
-
38th COSPAR Scientific Assembly
- Pub Date:
- 2010
- Bibcode:
- 2010cosp...38.1855D