Disentangling flows in the solar transition region

Zacharias, P.; Hansteen, V. H.; Leenaarts, J.; Carlsson, Mats; Gudiksen, B. V.

doi:10.1051/0004-6361/201732055

Cited by 15 publications

(15 citation statements)

References 31 publications

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“…Hansteen et al (2010) expanded on this model and injected an emerging flux to the 3D model of Peter et al (2006) and concluded that these downflows are a result of the rapid episodical heating between the upper chromosphere and lower corona. Zacharias et al (2018) further complemented these earlier studies by establishing that pressure driven downflows along the magnetic field lines could be identified as one of the key mechanisms responsible for these observed red shifts in the TR.…”

Section: What Might Cause Downflowing Rres?mentioning

confidence: 54%

Spicules and downflows in the solar chromosphere

Bose

Joshi

Henriques

et al. 2021

A&A

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Context. High-speed downflows have been observed in the solar transition region (TR) and lower corona for many decades. Despite their abundance, it has been hard to find signatures of such downflows in the solar chromosphere. Aims. In this work, we target an enhanced network region which shows ample occurrences of rapid spicular downflows in the Hα spectral line, which could potentially be linked to high-speed TR downflowing counterparts. Methods. We used the k-means algorithm to classify the spectral profiles of on-disk spicules in Hα and Ca II K data observed from the Swedish 1 m Solar Telescope and employed an automated detection method based on advanced morphological image processing operations to detect such downflowing features, in conjunction with rapid blue-shifted and red-shifted excursions (RBEs and RREs). Results. We report the existence of a new category of RREs (termed as downflowing RRE) for the first time that, contrary to earlier interpretation, are associated with chromospheric field aligned downflows moving toward the strong magnetic field regions. Statistical analysis performed on nearly 20 000 RBEs and 15 000 RREs (including the downflowing counterparts), which were detected in our 97 min long dataset, shows that the downflowing RREs are very similar to RBEs and RREs except for their oppositely directed plane-of-sky motion. Furthermore, we also find that RBEs, RREs, and downflowing RREs can be represented by a wide range of spectral profiles with varying Doppler offsets, and Hα line core widths, both along and perpendicular to the spicule axis, that causes them to be associated with multiple substructures which evolve together. Conclusions. We speculate that these rapid plasma downflows could well be the chromospheric counterparts of the commonly observed TR downflows.

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Section: What Might Cause Downflowing Rres?mentioning

confidence: 54%

Spicules and downflows in the solar chromosphere

Bose

Joshi

Henriques

et al. 2021

A&A

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“…We ask how the heating in the coronal loops and their foopoints in the chromosphere could lead to a heating of the chromospheric loops. A plausible mechanism is through radiative heating, in which the Ly-α line is the main source together with heating from EUV optically thin radiative losses from the transition region and corona absorbed in the chromosphere (for details see Zacharias et al 2018). To confirm this further numerical simulations are required.…”

Section: Discussionmentioning

confidence: 99%

The chromospheric component of coronal bright points

Madjarska

Chae

Moreno‐Insertis

et al. 2021

A&A

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Context. We investigate the chromospheric counterpart of small-scale coronal loops constituting a coronal bright point (CBP) and its response to a photospheric magnetic-flux increase accompanied by co-temporal CBP heating. Aims. The aim of this study is to simultaneously investigate the chromospheric and coronal layers associated with a CBP, and in so doing, provide further understanding on the heating of plasmas confined in small-scale loops. Methods. We used co-observations from the Atmospheric Imaging Assembly and Helioseismic Magnetic Imager on board the Solar Dynamics Observatory, together with data from the Fast Imaging Solar Spectrograph taken in the Hα and Ca II 8542.1 Å lines. We also employed both linear force-free and potential field extrapolation models to investigate the magnetic topology of the CBP loops and the overlying corona, respectively. We used a new multi-layer spectral inversion technique to derive the temporal variations of the temperature of the Hα loops (HLs). Results. We find that the counterpart of the CBP, as seen at chromospheric temperatures, is composed of a bundle of dark elongated features named in this work Hα loops, which constitute an integral part of the CBP loop magnetic structure. An increase in the photospheric magnetic flux due to flux emergence is accompanied by a rise of the coronal emission of the CBP loops, that is a heating episode. We also observe enhanced chromospheric activity associated with the occurrence of new HLs and mottles. While the coronal emission and magnetic flux increases appear to be co-temporal, the response of the Hα counterpart of the CBP occurs with a small delay of less than 3 min. A sharp temperature increase is found in one of the HLs and in one of the CBP footpoints estimated at 46% and 55% with respect to the pre-event values, also starting with a delay of less than 3 min following the coronal heating episode. The low-lying CBP loop structure remains non-potential for the entire observing period. The magnetic topological analysis of the overlying corona reveals the presence of a coronal null point at the beginning and towards the end of the heating episode. Conclusions. The delay in the response of the chromospheric counterpart of the CBP suggests that the heating may have occurred at coronal heights.

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“…Fig1 shows a snapshot of the experimental setup. As in Carlsson et al (2016); Leenaarts et al (2012Leenaarts et al ( , 2015; Zacharias et al (2018), the magnetic field in the photosphere is a predominantly bipolar structure seen as two clusters of magnetic concentrations of opposite polarity. This field was introduced into the simulation by specifying the vertical magnetic field at the bottom boundary with an averaged signed field of zero and two patches of opposite polarity separated by 8 Mm.…”

Section: Bifrost Experiments Descriptionmentioning

confidence: 93%

“…The corks module (Leenaarts 2018;Zacharias et al 2018) uses passive tracer particles to present the Lagrangian frame, flowing with the mass elements present. In particular the corks module is accurate and versatile because the cork positions are updated on the time-steps of the MHD simulations, rather than using saved data that is stored at intervals much greater than the simulation time-steps (Shelyag et al 2013;Nóbrega-Siverio et al 2016).…”

Section: Appendix A: Corks Module Detailsmentioning

confidence: 99%

The formation and heating of chromospheric fibrils in a radiation-MHD simulation

Druett,

Leenaarts,

Carlsson

et al. 2021

Preprint

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Aims. We examine the movements of mass elements within dense fibrils using passive tracer particles (corks) in order to understand fibril creation and destruction processes. Methods. Simulated fibrils were selected at times when they were visible in an Hα image proxy. The corks were selected within fibril Hα formation regions. From this set, a cork was selected, and the field line passing through it was constructed. Other fibrilar corks close to this fieldline were also selected. Pathlines were constructed, revealing the locations of the mass elements forward and backward in time. The forces acting on these mass elements were analysed. Results. The main process of fibrilar loading in the simulation is different to the mass loading scenario in which waves steepen into shocks and push material upwards along the fieldlines from near their footpoints. Twisted low lying fieldlines were destabilised and then they untwisted, lifting the material trapped above their apexes via the Lorentz force. Subsequently, the majority of the mass drained down the fieldlines towards one or both footpoints under gravity. Material with large horizontal velocities could also elevated in rising fieldlines, creating somewhat parabolic motions, but material was not generally moving upward along a stationary magnetic fieldline during loading. Conclusions. The processes observed in the simulation are plausible additional scenarios. Criteria for observing such events are described. It is desirable that our simulations can also form more densely-packed fibrils from material fed from the base of field footpoints. Experimental parameters required to achieve this are discussed.

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Disentangling flows in the solar transition region

Cited by 15 publications

References 31 publications

Spicules and downflows in the solar chromosphere

Spicules and downflows in the solar chromosphere

The chromospheric component of coronal bright points

The formation and heating of chromospheric fibrils in a radiation-MHD simulation

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