Helical Motions of Fine-Structure Prominence Threads Observed by Hinode and Iris

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 activeregion prominences observed by the Hinode and/or 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 ∼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.

Solar prominences: theory and models

“…(2009), who observed a whole prominence rotating about its spine, and by Okamoto et al. (2016), who observed a small part of a prominence spine rotating and interpreted it as magnetic reconnection between flux systems (Fig. 16).…”

Quiescent Prominence Dynamics Observed with the Hinode Solar Optical Telescope. II. Prominence Bubble Boundary Layer Characteristics and the Onset of a Coupled Kelvin–Helmholtz Rayleigh–Taylor Instability

“…Xia and Keppens (2016) model the quiescent prominence formation process numerically to confirm that hot plasma is transported upward from the chromosphere by dynamic flows, while radiatively cooled plasma returns to the chromosphere in the form of the ubiquitous vertical filamentary downflows (Engvold 1981;Berger et al 2008). Analysis of plasma motions in the "coronal cavities" associated with magnetic flux ropes (Fuller and Gibson 2009;Schmit and Gibson 2011;Dove et al 2011;Li et al 2012;Bak-Steślicka et al 2013;Panesar et al 2013) and in the prominences themselves (Okamoto et al 2009(Okamoto et al , 2016) support the proposition that flows from the lower atmosphere transport plasma and magnetic flux into system. If confirmed, small-scale emerging flux regions could represent a source term in the so-called "chromosphere-corona mass cycle" (Marsch et al 2008;Berger et al 2011;McIntosh et al 2012) in which hot plasma is transported upward into the corona while radiatively cooled plasma is channelled by magnetic fields to form visible cool plasma return flows in prominences (e.g., Low et al 2012a,b;Berger et al 2012;Xia and Keppens 2016) or coronal rain (Antolin and Rouppe van der Voort 2012).…”

The magnetic Rayleigh–Taylor instability in solar prominences

“…The dynamics of this prominence are analysed in Okamoto et al (2016) the solar disk. While prominences are seen as features in emission in spectral lines at the solar limb, on the solar disk they appear as dark absorption features.…”

“…For active region prominences, they are likely to be dominated by field aligned flows and magnetohydrodynamic (MHD) waves (e.g. Okamoto et al 2007) in the horizontal threads, but also can show winding motions (Okamoto et al 2016). Active region prominences are more eruptive, and as such have shorter lifetimes, but quiescent prominences can remain in the corona for weeks.…”