Helical motions of fine-structure prominence threads observed by Hinode and IRIS

TL;DR

This paper presents high-resolution observations of helical rotational motions in solar prominence threads, revealing their dynamics, propagation of twists, and potential magnetic reconnection mechanisms, advancing understanding of prominence physics and space weather impacts.

Contribution

It provides the first detailed evidence of rotational motions in prominence threads observed simultaneously in multiple wavelengths, linking these motions to magnetic reconnection processes.

Findings

Transverse motions with speeds up to 55 km/s suggest rotational dynamics.

Propagation of twists along threads at phase speeds of 90–270 km/s.

Doppler velocities indicate opposite directions of motion in prominence regions.

Abstract

Fine-structure dynamics in solar prominences holds critical clues to understanding their physical nature of significant space-weather implications. We report evidence of rotational motions of horizontal helical threads in two active-region prominences observed by the \emph{Hinode} and/or \emph{IRIS} satellites at high resolution. In the first event, we found transverse motions of brightening threads at speeds up to 55~km~s$^{-1}$ seen in the plane of the sky. Such motions appeared as sinusoidal space--time trajectories with a typical period of $\sim$390~s, which is consistent with plane-of-sky projections of rotational motions. Phase delays at different locations suggest propagation of twists along the threads at phase speeds of 90--270~km~s$^{-1}$. At least 15 episodes of such motions occurred in two days, none associated with any eruption. For these episodes, the plane-of-sky speed is linearly correlated with the vertical travel distance, suggestive of a constant angular speed. In the second event, we found Doppler velocities of 30--40~km~s$^{-1}$ in opposite directions in the top and bottom portions of the prominence, comparable to the plane-of-sky speed. The moving threads have about twice broader line widths than stationary threads. These observations, when taken together, provide strong evidence for rotations of helical prominence threads, which were likely driven by unwinding twists triggered by magnetic reconnection between twisted prominence magnetic fields and ambient coronal fields.