Mystery of Solar Flux ropes
Coronal mass ejections show twisted magnetic field structure. Such tubes of twisted magnetic fields are called as flux ropes and they can store plenty of free magnetic energy in the corona. The questions when and how the flux ropes form have puzzled scientists for decades. In some cases magnetic fields may survive twisted deeper from the Sun, but mostly the flux ropes that are integral part of erupting coronal mass ejections are believed to form in the solar corona. However, it is not clear yet whether the flux rope typically forms prior to the eruption or during the eruption process. The plasma instabilities and processes that trigger and drive the eruption are also largely unknown.
In this Solar Physics paper led by Alexander James from Mullard Space Science Laboratory we combined a wide variety of observations (e.g., EUV, radio and magnetograms) to analyse the formation and eruption of a flux rope on June 14, 2012. We found that magnetic reconnection formed the flux rope a few hours before its eruption in the corona. This was consistent also with plasma composition analysis suggesting the existence of coronal plasma in the flux rope. This eruption originated from an emerging active region where vortical motions of the flux rope footpoints caused it to rise and become hence unstable. The paper also highlights the importance of combining different observations for shedding light on how solar eruptions form.
Left) Sigmoidal Extreme Ultraviolet structure signalling the flux rope, Right) associated coronal mass ejection detected by coronagraph onboard STEREO-A