A solar tornado triggered by flares?

Abstract

Context. Solar tornados are dynamical, conspicuously helical magnetic structures that are mainly observed as a prominence activity. Aims. We investigate and propose a triggering mechanism for the solar tornado observed in a prominence cavity by SDO/AIA on September 25, 2011. Methods. High-cadence EUV images from the SDO/AIA and the Ahead spacecraft of STEREO/EUVI are used to correlate three flares in the neighbouring active-region (NOAA 11303) and their EUV waves with the dynamical developments of the tornado. The timings of the flares and EUV waves observed on-disk in 195 Å are analysed in relation to the tornado activities observed at the limb in 171 Å. 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.

DYNAMICS OF A SOLAR PROMINENCE TORNADO OBSERVED BYSDO/AIA ON 2012 NOVEMBER 7–8

“…This process extends for an hour and the tornado gradually follows the cavity. Expansion of coronal cavities have been also reported by various authors (Li et al 2012;Panesar et al 2013) and they estimated the expansion speed as ∼ 2.5 km s −1 . The instability of cavity prominences can be explained by the magnetic breakout model (Antiochos et al 1999;Aulanier et al 2000;Maia et al 2003;Shen et al 2012).…”

“…The upward expansion of a twisted tornado may also cause an apparent transverse displacement of the tornado axis (Panesar et al 2013;Panasenco et al 2014). The second oscillation pattern can be hardly explained by this mechanism, because the tornado was not rising during the interval of oscillation.…”

Two Solar Tornadoes Observed with the Interface Region Imaging Spectrograph

“…Su et al (2012) found that the rotating solar tornadoes observed with SDO/AIA have a connection with prominences. The pos-sible relationship between a solar tornado and CMEs/flares from the surrounding active region has also been reported (Panesar et al 2013). Wedemeyer-Böhm et al (2013) performed a statistical analysis of tornadoes using SDO/AIA observations and found that these solar tornadoes, which they called giant tornadoes, have a close relationship with prominences, share some similar characteristics with barbs and may serve as the plasma source of some prominences.…”

Automated Swirl Detection Algorithm (ASDA) and Its Application to Simulation and Observational Data

“…Rotational motions have been observed on the Sun on a variety of scales, including sub-arcsecond vortex flows (Bonet et al 2008), large-scale sunspot rotations (Evershed 1910;Brown et al 2003), tornadoes (Li et al 2012;Wedemeyer-Böhm et al 2012;Su et al 2012;Panesar et al 2013;Wang et al 2016), spicules/jets (Kitiashvili et al 2013;Liu et al 2009Liu et al , 2014 and even coronal mass ejections (CMEs) (Vourlidas et al 2011). The small-scale photospheric vortices are widely hypothesised to form as a natural consequence to granular flows (Wang et al 1995;Attie et al 2009) in the quiet Sun and could play a key role in the supply of energy to the upper solar atmosphere either, for example, through the build up of magnetic energy in twisted field lines in the corona or through the channeling of magneto-hydrodynamic (MHD) waves (Velli & Liewer 1999;Shelyag et al , 2013.…”