Apparent Solar Tornado - Like Prominences

TL;DR

High-resolution solar observations show that tornado-like prominences are illusions caused by projection effects and plasma motions, not true vortical structures, clarifying their nature and relation to magnetic fields and photospheric vortices.

Contribution

This study clarifies that solar tornado-like prominences are illusions due to projection effects and plasma motions, not actual vortices, based on high-resolution SDO data.

Findings

Tornado appearances are due to projection effects and plasma motions.

Apparent vortical motions arise from counterstreaming and oscillations.

No evidence of true vortical motion in tornado prominences.

Abstract

Recent high-resolution observations from the Solar Dynamics Observatory (SDO) have reawakened interest in the old and fascinating phenomenon of solar tornado-like prominences. This class of prominences was first introduced by Pettit (1932), who studied them over many years. Observations of tornado prominences similar to the ones seen by SDO had already been documented by Secchi (1877) in his famous "Le Soleil". High resolution and high cadence multiwavelength data obtained by SDO reveal that the tornado-like appearance of these prominences is mainly an illusion due to projection effects. We discuss two different cases where prominences on the limb might appear to have a tornado-like behavior. One case of apparent vortical motions in prominence spines and barbs arises from the (mostly) 2D counterstreaming plasma motion along the prominence spine and barbs together with oscillations along individual threads. The other case of apparent rotational motion is observed in prominence cavities and results from the 3D plasma motion along the writhed magnetic fields inside and along the prominence cavity as seen projected on the limb. Thus, the "tornado" impression results either from counterstreaming and oscillations or from the projection on the plane of the sky of plasma motion along magnetic field lines, rather than from a true vortical motion around an (apparent) vertical or horizontal axis. We discuss the link between tornado-like prominences, filament barbs, and photospheric vortices at their base.