High-resolution observations of the solar photosphere, chromosphere, and transition region

Waves and oscillations have been observed in the Sun’s atmosphere for over half a century. While such phenomena have readily been observed across the entire electromagnetic spectrum, spanning radio to gamma-ray sources, the underlying role of waves in the supply of energy to the outermost extremities of the Sun’s corona has yet to be uncovered. Of particular interest is the lower solar atmosphere, including the photosphere and chromosphere, since these regions harbor the footpoints of powerful magnetic flux bundles that are able to guide oscillatory motion upwards from the solar surface. As a result, many of the current- and next-generation ground-based and space-borne observing facilities are focusing their attention on these tenuous layers of the lower solar atmosphere in an attempt to study, at the highest spatial and temporal scales possible, the mechanisms responsible for the generation, propagation, and ultimate dissipation of energetic wave phenomena. Here, we present a two-fold review that is designed to overview both the wave analyses techniques the solar physics community currently have at their disposal, as well as highlight scientific advancements made over the last decade. Importantly, while many ground-breaking studies will address and answer key problems in solar physics, the cutting-edge nature of their investigations will naturally pose yet more outstanding observational and/or theoretical questions that require subsequent follow-up work. This is not only to be expected, but should be embraced as a reminder of the era of rapid discovery we currently find ourselves in. We will highlight these open questions and suggest ways in which the solar physics community can address these in the years and decades to come.

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Waves in the lower solar atmosphere: the dawn of next-generation solar telescopes

Jess

Jafarzadeh

Keys

et al. 2023

Living Rev Sol Phys

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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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Signatures of ubiquitous magnetic reconnection in the deep atmosphere of sunspot penumbrae

Voort

Joshi

Henriques

et al. 2021

A&A

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Context. Ellerman bombs are regions with enhanced Balmer line wing emission and mark magnetic reconnection in the deep solar atmosphere in active regions and the quiet Sun. They are often found in regions where opposite magnetic polarities are in close proximity. Recent high-resolution observations suggest that Ellerman bombs are more prevalent than previously thought. Aims. We aim to determine the occurrence of Ellerman bombs in the penumbra of sunspots. Methods. We analyzed high spatial resolution observations of sunspots in the Balmer Hα and Hβ lines as well as auxiliary continuum channels obtained with the Swedish 1-m Solar Telescope and applied the k-means clustering technique to systematically detect and characterize Ellerman Bombs. Results. Features with all the defining characteristics of Ellerman bombs are found in large numbers over the entire penumbra. The true prevalence of these events is only fully appreciated in the Hβ line due to the highest spatial resolution and lower chromospheric opacity. We find that the penumbra hosts some of the highest Ellerman bomb densities, surpassed only by the moat in the immediate surroundings of the sunspot. Some penumbral Ellerman bombs show flame morphology and rapid dynamical evolution. Many penumbral Ellerman bombs are fast moving with typical speed of 3.7 km s−1 and sometimes more than 10 km s−1. Many penumbral Ellerman bombs migrate from the inner to the outer penumbra over hundreds of km, and some continue moving beyond the outer penumbral boundary into the moat. Many penumbral Ellerman bombs are found in the vicinity of regions with opposite magnetic polarity. Conclusions. We conclude that reconnection is a near continuous process in the low atmosphere of the penumbra of sunspots that manifest in the form of penumbral Ellerman bombs. These are so prevalent that they may be a major sink of sunspot magnetic energy.

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High-resolution observations of the solar photosphere, chromosphere, and transition region

Cited by 11 publications

References 42 publications

Waves in the lower solar atmosphere: the dawn of next-generation solar telescopes

Waves in the lower solar atmosphere: the dawn of next-generation solar telescopes

Spicules and downflows in the solar chromosphere

Signatures of ubiquitous magnetic reconnection in the deep atmosphere of sunspot penumbrae

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