Propagating brightenings in small loop-like structures in the quiet-Sun corona: Observations from Solar Orbiter/EUI

Mandal, Sudip; Peter, Hardi; Chitta, L. P.; Solanki, S. K.; Cuadrado, R. Aznar; Teriaca, L.; Schühle, U.; Berghmans, David; Auchère, F.

doi:10.1051/0004-6361/202142041

Cited by 23 publications

(30 citation statements)

References 43 publications

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“…In their study, the 3D magnetic field structures of the component reconnection are very similar to the tethercutting type in our study. Observationally, such a tethercutting-like structure was also confirmed to interpret other small-scale transient brightenings similar to campfires (e.g., Chitta et al 2021;Mandal et al 2021). Moreover, we also estimate the heights of the microflares, which range from 2 to 10 Mm above the photosphere, similar to that of campfires (Berghmans et al 2021).…”

Section: Summary and Discussionsupporting

confidence: 83%

Three-dimensional Magnetic and Thermodynamic Structures of Solar Microflares

Cheng

Chen

et al. 2022

ApJL

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Microflares, one of the small-scale solar activities, are believed to be caused by magnetic reconnection. Nevertheless, their three-dimensional (3D) magnetic structures, thermodynamic structures, and physical links to reconnection are unclear. In this Letter, based on a high-resolution 3D radiative magnetohydrodynamic simulation of the quiet Sun spanning from the upper convection zone to the corona, we investigate the 3D magnetic and thermodynamic structures of three homologous microflares. It is found that they originate from localized hot plasma embedded in the chromospheric environment at the height of 2–10 Mm above the photosphere and last for 3–10 minutes with released magnetic energy in the range of 1027–1028 erg. The heated plasma is almost cospatial with the regions where the heating rate per particle is maximal. The 3D velocity field reveals a pair of converging flows with velocities of tens of km s−1 moving toward and outflows with velocities of about 100 km s−1 moving away from the hot plasma. These features support magnetic reconnection playing a critical role in heating the localized chromospheric plasma to coronal temperature, giving rise to the observed microflares. The magnetic topology analysis further discloses that the reconnection region is located near quasi-separators where both current density and squashing factors are maximal although the specific topology may vary from a tether-cutting to fan-spine-like structure.

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Section: Summary and Discussionsupporting

confidence: 83%

Three-dimensional Magnetic and Thermodynamic Structures of Solar Microflares

Cheng

Chen

et al. 2022

ApJL

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“…Besides, we found a SBP that is induced by the primary UBP, and the converging motion along a large loop-like structure is found between their moving structures. The moving structures observed in UBPs seem to be similar to the propagating brightenings reported by Mandal et al (2021). However, the merger-type event of propagating brightenings started at one footpoint and moved toward another footpoint, and their repeated plasma ejections showed the uni-directional motion (see Mandal et al 2021).…”

Section: Conclusion and Discussionsupporting

confidence: 68%

“…In this case, we investigated a UBP (labeled 'BP2') showing converging motions between a pair of moving structures, as shown in Figure 6. Different from the 'BP1', it firstly brightens at about 12:13:45 UT at two separated positions, which might be regarded as the two footpoints of a loop structure (cf., Mandal et al 2021). Then they gradually move to their center position such as the loop top along a curved path between 12:14:00−12:14:45 UT.…”

Section: Converging Motions Between the Moving Structuresmentioning

confidence: 99%

“…In the Solar Orbiter (SolO; Müller et al 2020) era, using High Resolutions (HRI) Telescopes of the Extreme Ultraviolet Imager (EUI; Rochus et al 2020), three groups of small-scale brightening events in the quiet Sun are reported. One group is named as 'campfire' (Berghmans et al 2021;Mandal et al 2021;Zhukov et al 2021), it could be driven by the component reconnection, e.g., loops reconnecting at coronal heights (Chen et al 2021;Panesar et al 2021). The second one is 'microjet', which is mostly likely produced by the low height reconnection with small-scale chromospheric fields.…”

Section: Introductionmentioning

confidence: 99%

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Moving structures in ultraviolet bright points: observations from Solar Orbiter/EUI

2022

Preprint

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Context. Moving structures have been detected in coronal bright points and in a solar flare in active regions, which were bi-directional, symmetrical, simultaneous, and quasi-periodic (Ning & Guo 2014;Ning 2016;Li et al. 2016a). They could be regarded as observational evidence of plasma outflows via magnetic reconnection. Aims. We explored pairs of moving structures in fifteen ultraviolet bright points (UBPs), which were observed in the quiet Sun or inside a small active region on 19 November 2020. Methods. The UBPs were measured by the High Resolution (HRI) Telescopes of the Extreme Ultraviolet Imager (EUI) on board the Solar Orbiter (SolO) in two passbands, HRI EUV 174 Å and HRI Lyα 1216 Å. The pairs of moving structures are identified in timedistance slices along curved slits of UBPs, and their quasi-periods are determined from the fast Fourier transform and wavelet analysis method.Results. Moving structures observed in ten UBPs as starting from their bright cores and propagating toward two ends, are interpreted as diverging motions of bi-directional moving structures. These moving structures are also characterized by simultaneity and symmetry and in the case of seven UBPs they exhibit quasi-periodicity. Moving structures seen in another five UBPs as originating from double ends and moving closer, and merging together, are manifested as converging motions. A sympathetic UBP induced by the primary UBP is observed at the edge of a small active region, and their moving structures also show the converging motion. Conclusions. The diverging motions of bi-directional moving structures could be generated by outflows after magnetic reconnections. The converging motions of two moving structures might be caused by inflows through the magnetic reconnection, or might be interpreted as upflows driven by the chromospheric evaporation.

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“…These speeds are consistent with those in observations (estimated for 20 randomly selected dots). These intensity propagation speeds are on the lower end of those found by Mandal et al (2021) for brightenings in a quiet solar coronal region and show similarities with loop-like and jet-like fine-scale explosive events seen by Hi-C 2.1 in an active region (Tiwari et al 2019). We note that dot 1 shows back-and-forth motion during its second and third frames (after its 50th second), after showing an initial displacement in the first 50 s. We took the speed along its path of the longest extension.…”

Section: Proper Motion Of Dots and The Speed Of Intensity Propagation...mentioning

confidence: 63%

SolO/EUI Observations of Ubiquitous Fine-scale Bright Dots in an Emerging Flux Region: Comparison with a Bifrost MHD Simulation

Tiwari

Hansteen

Pontieu

et al. 2022

ApJ

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We report on the presence of numerous tiny bright dots in and around an emerging flux region (an X-ray/coronal bright point) observed with SolO’s EUI/HRIEUV in 174 Å. These dots are roundish and have a diameter of 675 ± 300 km, a lifetime of 50 ± 35 s, and an intensity enhancement of 30% ± 10% above their immediate surroundings. About half of the dots remain isolated during their evolution and move randomly and slowly (<10 km s−1). The other half show extensions, appearing as a small loop or surge/jet, with intensity propagations below 30 km s−1. Many of the bigger and brighter HRIEUV dots are discernible in the SDO/AIA 171 Å channel, have significant emissivity in the temperature range of 1–2 MK, and are often located at polarity inversion lines observed in SDO/HMI LOS magnetograms. Although not as pervasive as in observations, a Bifrost MHD simulation of an emerging flux region does show dots in synthetic Fe ix/x images. These dots in the simulation show distinct Doppler signatures—blueshifts and redshifts coexist, or a redshift of the order of 10 km s−1 is followed by a blueshift of similar or higher magnitude. The synthetic images of O v/vi and Si iv lines, which represent transition region radiation, also show the dots that are observed in Fe ix/x images, often expanded in size, or extended as a loop, and always with stronger Doppler velocities (up to 100 km s−1) than that in Fe ix/x lines. Our observation and simulation results, together with the field geometry of dots in the simulation, suggest that most dots in emerging flux regions form in the lower solar atmosphere (at ≈ 1 Mm) by magnetic reconnection between emerging and preexisting/emerged magnetic field. Some dots might be manifestations of magnetoacoustic shocks through the line formation region of Fe ix/x emission.

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Propagating brightenings in small loop-like structures in the quiet-Sun corona: Observations from Solar Orbiter/EUI

Cited by 23 publications

References 43 publications

Three-dimensional Magnetic and Thermodynamic Structures of Solar Microflares

Three-dimensional Magnetic and Thermodynamic Structures of Solar Microflares

Moving structures in ultraviolet bright points: observations from Solar Orbiter/EUI

SolO/EUI Observations of Ubiquitous Fine-scale Bright Dots in an Emerging Flux Region: Comparison with a Bifrost MHD Simulation

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