Magnetic flux ropes as a trigger for solar eruptions

Observations of the formation and evolution of a magnetic flux rope on the surface of the Sun before and during a solar eruption are presented in Nature Communications this week. The findings suggest that eruptions, such as solar flares, are not spontaneous but are instead caused by instabilities in the flux rope. Magnetic flux ropes - formed in plasmas - are current channels with helical magnetic field lines wrapped around them. They are thought to be important to explosive phenomena like coronal mass ejections, although direct evidence has remained elusive. Jie Zhang and co-workers used observations from the Atmospheric Imaging Assembly telescope on the Solar Dynamics Observatory to study a solar eruption on 8 March 2011. Using multi-temperature images, they saw the formation of a giant twisted flux rope, which grew outwards before accelerating up and reconnecting with the surface, coinciding with the onset of a solar flare. The new data provide evidence that the flare does not happen spontaneously but is triggered by the macroscopic motion of the flux rope. This finding may extend beyond solar eruptions to other plasma systems.