Abstract
Abstract Bubbles, the semi-circular voids below quiescent prominences (filaments), have been extensively investigated in the past decade. However, to this point the magnetic nature of bubbles has been unverifiable due to the lack of on-disk photospheric magnetic field observations. Here for the first time, we find and investigate an on-disk prominence bubble around a filament barb on 2019 March 18 based on stereoscopic observations from the New Vacuum Solar Telescope (NVST), Solar Dynamics Observatory (SDO), and Spacecraft-A of the Solar TErrestrial RElations Observatory (STEREO-A). In high-resolution NVST Hα images, this bubble has a sharp arch-like boundary and a projected width of ∼26 Mm. Combining SDO and STEREO-A images, we further reconstruct 3D structure of the bubble boundary, whose maximum height is ∼15.6 Mm. The squashing factor Q map deduced from extrapolated 3D magnetic fields around the bubble depicts a distinct arch-shaped interface with a height of ∼11 Mm, which agrees well with the reconstructed 3D structure of the observed bubble boundary. Under the interface lies a set of magnetic loops, which is rooted on a surrounding photospheric magnetic patch. To be more persuasive, another on-disk bubble on 2019 June 10 is presented as a supplement. According to these results obtained from on-disk bubble observations, we suggest that the bubble boundary corresponds to the interface between the prominence dips (barb) and the underlying magnetic loops rooted nearby. Therefore, it is reasonable to speculate that the bubble can form around a filament barb below which there is a photospheric magnetic patch.
Highlights
For the first time, we find and investigate an on-disk prominence bubble around a filament barb on 2019 March 18 based on stereoscopic observations from New Vacuum Solar Telescope (NVST), Solar Dynamics Observatory (SDO), and STEREO-A
According to these results obtained from on-disk bubble observations, we suggest that the bubble boundary corresponds to the interface between the prominence dips and the underlying magnetic loops rooted nearby
In STEREO-A 171 ̊A and 195 ̊A images, this structure is located near solar west limb and presents typical features of the prominence bubble below the barb, which appears as a vertical “tornado” structure (e.g., Su et al 2012; Wedemeyer et al 2013), (Figures 1(d1) and (d2))
Summary
Solar prominences are cool and dense plasma structure suspended in hot and tenuous corona. Recent highresolution observations reveal that dark “bubbles” with bright arch-like boundaries are formed below prominences, and small-scale upward “plumes” are usually detected above the bubble boundaries (Berger et al 2008, 2010). These plumes might be caused by Rayleigh-Taylor instability (Berger et al 2010; Ryutova et al 2010; Hillier et al 2011, 2012), coupled Kelvin-Helmholtz Rayleigh-Taylor instability (Berger et al 2017; Mishra & Srivastava 2019) or magnetic reconnection (Dudık et al 2012; Gunar et al 2014; Shen et al 2015). The formation of bubbles is generally believed to closely connect with the emerging magnetic flux under the prominences (Berger et al 2011; Dudık et al 2012; Gunar et al 2014; Shen et al 2015). Another on-disk bubble is analyzed for a supplement
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