Subarcsecond bright points and quasi-periodic upflows below a quiescent filament observed by IRIS

Abstract

Context. The new Interface Region Imaging Spectrograph (IRIS) mission provides high-resolution observations of UV spectra and slit-jaw images (SJIs). These data have become available for investigating the dynamic features in the transition region (TR) below the on-disk filaments. Aims. The driver of "counter-streaming" flows along the filament spine is still unknown yet. The magnetic structures and the upflows at the footpoints of the filaments and their relations with the filament mainbody have not been well understood. We study the dynamic evolution at the footpoints of filaments in order to find some clues for solving these questions. Methods. Using UV spectra and SJIs from the IRIS, along with coronal images and magnetograms from the Solar Dynamics Observatory (SDO), we present the new features in a quiescent filament channel: subarcsecond bright points (BPs) and quasi-periodic upflows.Results. The BPs in the TR have a spatial scale of about 350−580 km and lifetimes of more than several tens of minutes. They are located at stronger magnetic structures in the filament channel with a magnetic flux of about 10 17 −10 18 Mx. Quasi-periodic brightenings and upflows are observed in the BPs, and the period is about 4−5 min. The BP and the associated jet-like upflow comprise a "tadpole-shaped" structure. The upflows move along bright filament threads, and their directions are almost parallel to the spine of the filament. The upflows initiated from the BPs with opposite polarity magnetic fields have opposite directions. The velocity of the upflows in the plane of sky is about 5−50 km s −1 . The emission line of Si IV 1402.77 Å at the locations of upflows exhibits obvious blueshifts of about 5−30 km s −1 , and the line profile is broadened with the width of more than 20 km s −1 . Conclusions. The BPs seem to be the bases of filament threads, and the upflows are able to convey mass for the dynamic balance of the filament. The "counter-streaming" flows in previous observations may be caused by the propagation of bi-directional upflows initiated from opposite polarity magnetic fields. We suggest that quasi-periodic brightenings of BPs and quasi-periodic upflows result from small-scale oscillatory magnetic reconnections, which are modulated by solar p-mode waves.

Solar Active Region Coronal Jets. II. Triggering and Evolution of Violent Jets

“…A similar such strand is discernible in a subsequent jetting episode in the video accompanying Figure 6(a) at times around 14:41:23 UT. When viewed against the disk however, filament material is apparently difficult to see in IRIS slit-jaw images, reportedly being semi-transparent and optically thin in 1330 Å and 1400 Å images (Li & Zhang 2016). Consistent with this, we see no absorbing filament material at those slit-jaw wavelengths, nor do we see any such material in the 2796 Å slit-jaw images.…”

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

“…. The high spatiotemporal resolution of IRIS has recently revealed evidence for injections of plasma into prominences through quasi-periodic reconnection (possibly mediated by p-mode oscillations) that lead to the well-known counterstreaming flows in prominences (Li and Zhang, 2016). Similar injection of plasma was observed by Zhao et al (2017)…”

Slipping Magnetic Reconnection of Flux-Rope Structures as a Precursor to an Eruptive X-Class Solar Flare

“…However, in AIA EUV images, both the dark and bright slipping structures are observed (arrows in Figures 3(c)-(d)). We suggest that the dark structures in 304 Å and 131 Å images correspond to filament materials, which are not evident in the optically thin lines such as 1400 Å and 1330 Å formed at transition region temperatures (Li & Zhang 2016). At about 15:53 UT, EUV brightenings were observed at the east footpoints of slipping structures (Figure 3(e)).…”