A solar tornado triggered by flares

The timings of the flares and EUV waves observed on-disk in 195 Ã are analysed in relation to the tornado activities observed at the limb in 171 Ã . Results. Each of the three flares and its related EUV wave occurred within ten hours of the onset of the tornado.

They have an observed causal relationship with the commencement of activity in the prominence where the tornado develops. Tornado-like rotations along the side of the prominence start after the second flare. The prominence cavity expands with the accelerating tornado motion after the third flare.

Conclusions. Flares in the neighbouring active region may have affected the cavity prominence system and triggered the solar tornado. A plausible mechanism is that the active-region coronal field contracted by the "Hudson effect" through the loss of magnetic energy as flares.

Subsequently, the cavity expanded by its magnetic pressure to fill the surrounding low corona. We suggest that the tornado is the dynamical response of the helical prominence field to the cavity expansion.