Two Solar Tornadoes Observed with the Interface Region Imaging Spectrograph

TL;DR

This study uses spectroscopic data from IRIS to analyze two solar tornadoes, providing evidence that they are indeed rotating cool plasma structures, and highlights the importance of spectroscopy in understanding prominence dynamics.

Contribution

First spectroscopic confirmation of rotating plasma in solar tornadoes, clarifying their physical nature and supporting the rotation interpretation over oscillation or flows.

Findings

Coherent Doppler shifts indicate rotation in tornadoes

Periodic dark structures support rotating plasma interpretation

Spectroscopy helps distinguish physical processes in prominences

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~{\sc{ii}}~k~2796\AA{}~and Si~{\sc{iv}}~1393\AA{}~line profiles. We find coherent and stable red and blue shifts 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.