A White-light Flare Powered by Magnetic Reconnection in the Lower Solar Atmosphere

Song, Yongliang; Zhu, Xiaoshuai; Chen, Yajie; Zhang, Mei; Zhang, Jingwen

doi:10.3847/2041-8213/ab83fa

Cited by 15 publications

(7 citation statements)

References 54 publications

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“…The low solar atmosphere is naturally a good laboratory for providing suitable opportunities to study magnetic reconnection in partially ionized plasma. Numerous small-scale events of reconnection in the low solar atmosphere have been observed in multi-wavelengths by advanced solar telescopes of high resolution and the fine structures of these events have also been recognized (e.g., Peter et al 2014;Xue et al 2016;Tian et al 2018;Huang et al 2018;Romano et al 2019;da Silva Santos et al 2020;Yan et al 2020;Song et al 2020;Joshi et al 2021;Rast et al 2021;Hou et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Plausibility of ultraviolet burst generation in the low solar chromosphere

Cheng

Lin

2022

A&A

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Context. Ultraviolet (UV) bursts and Ellerman bombs (EBs) are small-scale magnetic reconnection events taking place in the highly stratified, low solar atmosphere. The plasma density, reconnection mechanisms, radiative cooling and transfer processes clearly differ from one layer of the atmosphere to the next. In particular, EBs are believed to form in the upper photosphere or the low chromosphere. It is still not clear whether UV bursts have to be generated at a higher atmospheric layer than the EBs or whether both UV bursts and EBs can occur in the low chromosphere. Aims. We numerically studied the low β magnetic reconnection process around the solar temperature minimum region (TMR) by including more realistic physical diffusions and radiative cooling models. We aim to find out whether UV bursts may occur in the low chromosphere and to investigate the dominant mechanism that accounts for heating in the UV burst in the chromosphere. Methods. We used the single-fluid magnetohydrodynamic (MHD) code NIRVANA to perform the simulations. The time-dependent ionization degrees of hydrogen and helium are included in the code, which lead to a more realistic magnetic diffusion caused by electron-neutral collision and ambipolar diffusion. A more realistic radiative cooling model is also included in the simulations. The initial mass density and temperature are 1.66057 × 10 −6 kg m −3 and 4400 K, respectively, values that are typical for the plasma environment around TMR. Results. Our results in high resolution indicate that the plasmas in the reconnection region are heated up to more than 20, 000 K if the reconnecting magnetic field is as strong as 500 G, which suggests that UV bursts can be generated in the dense low chromosphere. The dominant mechanism for producing the UV burst in the low chromosphere is heating, as a result of the local compression in the reconnection process. The thermal energy occurring in the reconnection region rapidly increases after the turbulent reconnection mediated by plasmoids is invoked. The average power density of the generated thermal energy in the reconnection region can reach over 1000 erg cm −3 s −1 , which is comparable to the average power density accounting for a UV burst. With the strength of the reconnecting magnetic field exceeding 900 G, the width of the synthesized Si IV 1394 Å line profile with multiple peaks can reach up to 100 km s −1 , which is consistent with observations.

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Section: Introductionmentioning

confidence: 99%

Plausibility of ultraviolet burst generation in the low solar chromosphere

Cheng

Lin

2022

A&A

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“…With observations of the Interface Region Imaging Spectragraph (IRIS, De Pontieu et al 2014), Peter et al (2014) identified four UV bursts (UBs) and suggested that they might be produced by magnetic reconnection in U-shape structures during flux emergence in the lower solar atmosphere. Subsequent studies revealed that these UBs indeed mostly occur in emerging flux regions (e.g., Vissers et al 2015;Tian et al 2016Tian et al , 2018bNelson et al 2016;Young et al 2018;Chen et al 2019c) and that some of them are indeed associated with U-shape magnetic field structures (e.g., Grubecka et al 2016;Zhao et al 2017;Tian et al 2018a;Chen et al 2019b;Song et al 2020). The difference is that EBs and UBs are more likely related to magnetic reconnection occurring in the lower-atmosphere part of the U-shape structures, whereas the reconnection in our observations appears to occur in a relatively higher part (possibly the lower corona) of the U-shape structures.…”

Section: Discussionmentioning

confidence: 99%

Formation of solar coronal loops through magnetic reconnection in an emerging active region

Hou¹,

Chen²,

Zhu³

et al. 2021

Preprint

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Coronal loops are building blocks of solar active regions (ARs). However, their formation is not well understood. Here we present direct observational evidence for the formation of coronal loops through magnetic reconnection as new magnetic fluxes emerge to the solar atmosphere. Observations in the EUV passbands of SDO/AIA clearly show the newly formed loops following magnetic reconnection within a vertical current sheet. Formation of the loops is also seen in the H&#945; images taken by NVST. The SDO/HMI observations show that a positive-polarity flux concentration moves toward a negative-polarity one with a speed of ~0.5 km s-1&#160;before the apparent formation of coronal loops. During the formation of coronal loops, we found signatures of flux cancellation and subsequent enhancement of the transverse field between the two polarities. We have reconstructed the three-dimensional magnetic field structure through a magnetohydrostatic model, which shows field lines consistent with the loops in AIA images. Numerous bright blobs with a width of ~1.5 Mm appear intermittently in the current sheet and move upward with apparent velocities of ~80 km s-1. We have also identified plasma blobs moving to the footpoints of the newly formed large loops, with apparent velocities ranging from 30 to 50 km s-1. A differential emission measure analysis shows that the temperature, emission measure and density of the bright blobs are 2.5-3.5 MK, 1.1-2.3&#215;1028&#160;cm-5&#160;and 8.9-12.9&#215;109&#160;cm-3, respectively. Power spectral analysis of these blobs indicates that the magnetic reconnection is inconsistent with the turbulent reconnection scenario.

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“…The code has also been applied to study solar activities in the lower atmosphere such as Hα fibrils (Zhu et al 2016), small-scale filament (Wang et al 2016), ultraviolet burst (Zhao et al 2017;Tian et al 2018;Chen et al 2019), and blowout jet (Zhu et al 2017). Other applications focus on large-scale structures of the magnetic fields in the corona also show the robustness of the method (Song et al 2018;Miao et al 2018;Joshi et al 2019;Song et al 2020;Fu et al 2020).…”

Section: Mhd Relaxation Methodsmentioning

confidence: 99%

Magnetohydrostatic Modeling of the Solar Atmosphere

Zhu¹,

Neukirch²,

Wiegelmann³

2022

Preprint

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Understanding structures and evolutions of the magnetic fields and plasma in multiple layers on the Sun is very important. A force-free magnetic field which is an accurate approximation of the solar corona due to the low plasma β has been widely studied and used to model the coronal magnetic structure. While the force-freeness assumption is well satisfied in the solar corona, the lower atmosphere is not force-free given the high plasma β. Therefore, a magnetohydrostatic (MHS) equilibrium which takes into account plasma forces, such as pressure gradient and gravitational force, is considered to be more appropriate to describe the lower atmosphere. This paper reviews both analytical and numerical extrapolation methods based on the MHS assumption for calculating the magnetic fields and plasma in the solar atmosphere from measured magnetograms.

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A White-light Flare Powered by Magnetic Reconnection in the Lower Solar Atmosphere

Cited by 15 publications

References 54 publications

Plausibility of ultraviolet burst generation in the low solar chromosphere

Plausibility of ultraviolet burst generation in the low solar chromosphere

Formation of solar coronal loops through magnetic reconnection in an emerging active region

Magnetohydrostatic Modeling of the Solar Atmosphere

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A White-light Flare Powered by Magnetic Reconnection in the Lower Solar Atmosphere

Cited by 15 publications

References 54 publications

Plausibility of ultraviolet burst generation in the low solar chromosphere

Plausibility of ultraviolet burst generation in the low solar chromosphere

Formation of solar coronal loops through&#160;magnetic reconnection in an emerging active region

Magnetohydrostatic Modeling of the Solar Atmosphere

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Formation of solar coronal loops through magnetic reconnection in an emerging active region