Expanding and Contracting Coronal Loops as Evidence of Vortex Flows Induced by Solar Eruptions

Eruptive solar flares were predicted to generate large-scale vortex flows at both sides of the erupting magnetic flux rope. This process is analogous to a well-known hydrodynamic process creating vortex rings. The vortices lead to advection of closed coronal loops located at the peripheries of the flaring active region. Outward flows are expected in the upper part and returning flows in the lower part of the vortex. Here, we examine two eruptive solar flares, the X1.1-class flare SOL2012-03-05T03: 20 and the C3.5-class SOL2013-06-19T07:29. In both flares, we find that the coronal loops observed by the Atmospheric Imaging Assembly in its 171 angstrom, 193 angstrom, or 211 angstrom passbands show coexistence of expanding and contracting motions, in accordance with the model prediction. In the X-class flare, multiple expanding and contracting loops coexist for more than 35 minutes, while in the C-class flare, an expanding loop in 193 angstrom appears to be close by and cotemporal with an apparently imploding loop arcade seen in 171 angstrom. Later, the 193 angstrom loop also switches to contraction. These observations are naturally explained by vortex flows present in a model of eruptive solar flares.