First direct observation of a torsional Alfvén oscillation in the corona of the Sun
Torsional Alfvén waves are promising candidates for transporting energy from the solar surface into the corona and have been theoretically predicted for decades. However, their detection is notoriously difficult and so far has mostly relied on indirect signatures.
Imaging and spectral data from the space-based IRIS observatory has been used to study a surge of cool solar plasma in the corona above the East limb of the Sun. The surge has been triggered by the magnetic reconnection of open and closed magnetic fields. Using imaging and spectral information the tell-tale torsional signatures of plasma rotation of alternating sense have been revealed.
This discovery was made by Dr Petra Kohutova and Dr Clara Froment the University of Oslo's Rosseland Centre for Solar Physics and Dr Erwin Verwichte from the University of Warwick's Center for Fusion, Space and Astrophysics. The paper has been published this month as a letter in the journal of Astronomy and Astrophysics., and has been featured as a highlight. This study provides the first direct observational evidence that magnetic reconnection leads to the generation of large-scale torsional Alfvén waves in the solar corona.