Two Solar Tornadoes Observed with the Interface Region Imaging Spectrograph

Abstract

The barbs or legs of some prominences show an apparent motion of rotation, which are often termed solar tornadoes. It is under debate whether the apparent motion is a real rotating motion, or caused by oscillations or counter-streaming flows. We present analysis results from spectroscopic observations of two tornadoes by the Interface Region Imaging Spectrograph. Each tornado was observed for more than 2.5 hours. Doppler velocities are derived through a single Gaussian fit to the Mg ii k 2796Å and Si iv 1393Å line profiles. We find coherent and stable redshifts and blueshifts adjacent to each other across the tornado axes, which appears to favor the interpretation of these tornadoes as rotating cool plasmas with temperatures of 10 4 K-10 5 K. This interpretation is further supported by simultaneous observations of the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, which reveal periodic motions of dark structures in the tornadoes. Our results demonstrate that spectroscopic observations can provide key information to disentangle different physical processes in solar prominences.

On the Dynamic Nature of a Quiescent Prominence Observed by IRIS and MSDP Spectrographs

“…This may have been recognized only in a few prominences (Schmieder et al 2014b;Yang et al 2018). This study may be one of the few studies which uses spectroscopic data from different spectrographs (ground based and space instruments) to support the argument, and further suggests with spectral evidence the presence of multi-component structures along the LOS by the Doppler dimming effect (Heinzel et al 2015).…”

“…The dynamic nature of fine structures is so far difficult to explain with static modelings of magnetic field dips sustaining the prominence plasma (Aulanier & Démoulin 1998;Heinzel & Anzer 1999;Heinzel et al 2001;Gunár et al 2014). The interpretation of the apparent motions that we see in prominences: rising bubbles, plumes, horns, rotating tornadoes etc is still open for discussion (Berger et al 2008;Heinzel et al 2008;de Toma et al 2008;Berger et al 2010;Dudík et al 2012;Li et al 2012;Schmit & Gibson 2013;Su et al 2014;Levens et al 2015;Wedemeyer et al 2013;Wang et al 2016;Yang et al 2018). After the past ten years it starts to be clear that prominences have a 3D complex structure where each pixel represents an integration of emission of all the fine structures along any line of sight crossing the volume of the prominence.…”

A New View of the Solar Interface Region from the Interface Region Imaging Spectrograph (IRIS)

“…IRIS observations have also elucidated the cross-field coherence in dynamic evolution of these lightwalls, which has been associated with slipping reconnection (Hou et al, 2016b;Bai et al, 2019): the light-wall dynamics appear to be intimately tied to, and thus help reveal the overall changes in, magnetic topology during a flare. High-resolution spatial and temporal data from IRIS and SDO have been used to confirm the observation of signatures of magnetic reconnection and accompanying flux cancelation (Yang et al, 2018b) including two-loop interaction processes, plasma blob ejections, and sheet-like structures above the flux-cancelation sites. Further studies of the conditions that lead to reconnection using the rich IRIS data archive are key to go beyond case studies and establish how common these mechanisms are.…”

“…Su et al, 2012) and identified that such helical motions are often apparent, caused by LOS superposition, and thus they are perhaps not as good of a measure of helicity or eruptive potential as thought (Panasenco, Martin, and Velli, 2014;Schmieder et al, 2017). Meanwhile, as exceptions to this general trend, actual rotational motions were also revealed by Doppler measurements (Orozco Suárez, Asensio Ramos, and Trujillo Bueno, 2012), including those in two tornadoes detected by IRIS (Yang et al, 2018b). This suggests that there could be two separate classes of tornados involving either apparent or real rotational motions.…”

Tornado model for a magnetised plasma

“…This model may be used as a basis for parameterising observed solar tornadoes 19,20 and estimating, otherwise difficult to measure, magnetic twist profiles from azimuthal velocities.…”