Solar low-lying cool loops and their contribution to the transition region EUV output

Sasso, C.; Andretta, V.; Spadaro, D.; Susino, Roberto

doi:10.1051/0004-6361/201117580

Cited by 11 publications

(13 citation statements)

References 47 publications

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“…In terms of modelling, it would be interesting to see what onedimensional loop models would predict for very short loops that are heated to 1.5 MK or more, if that is possible. The models by Sasso et al (2012) produce transition region loops with temperatures well below 1 MK only. If, in those models, the energy input is increased, the loops might reach higher temperatures, and it would be interesting to see if they turn out to be stable or highly intermittent.…”

Section: Discussionmentioning

confidence: 99%

Miniature loops in the solar corona

Barczynski

Peter

Savage

2017

A&A

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Context. Magnetic loops filled with hot plasma are the main building blocks of the solar corona. Usually they have lengths of the order of the barometric scale height in the corona that is 50 Mm. Aims. Previously it has been suggested that miniature versions of hot loops exist. These would have lengths of only 1 Mm barely protruding from the chromosphere and spanning across just one granule in the photosphere. Such short loops are well established at transition region temperatures (0.1 MK), and we investigate if such miniature loops also exist at coronal temperatures (>1 MK). Methods. We used extreme UV imaging (EUV) observations from the High-resolution Coronal Imager (Hi-C) at an unprecedented spatial resolution of 0.3 to 0.4 . Together with EUV imaging and magnetogram data from the Solar Dynamics Observatory (SDO) and X-Ray Telescope (XRT) data from Hinode we investigated the spatial, temporal and thermal evolution of small loop-like structures in the solar corona above a plage region close to an active region and compared this to a moss area within the active region.Results. We find that the size, motion and temporal evolution of the loop-like features are consistent with photospheric motions, suggesting a close connection to the photospheric magnetic field. Aligned magnetograms show that one of their endpoints is rooted at a magnetic concentration. Their thermal structure, as revealed together with the X-ray observations, shows significant differences to moss-like features. Conclusions. Considering different scenarios, these features are most probably miniature versions of hot loops rooted at magnetic concentrations at opposite sides of a granule in small emerging magnetic loops (or flux tubes).

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Section: Discussionmentioning

confidence: 99%

Miniature loops in the solar corona

Barczynski

Peter

Savage

2017

A&A

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“…It has been found that, although heating by single pulses might explain the majority of DEMs derived in the literature (Bradshaw et al , 2010 ) and that trains of nanoflares might explain practically all of them (Reep et al , 2013 ), the uncertainties in the data analysis and DEM reconstruction are too large reach conclusive answers. Radiative losses are important to the existence of small and cool loops (height ≤ 8 Mm, T ≤ 10 5 K) that determine the cool side of the emission measure distribution (Sasso et al , 2012 ).…”

Section: Loop Physics and Modelingmentioning

confidence: 99%

Coronal Loops: Observations and Modeling of Confined Plasma

Reale

2014

Living Rev. Solar Phys.

295

265

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Coronal loops are the building blocks of the X-ray bright solar corona. They owe their brightness to the dense confined plasma, and this review focuses on loops mostly as structures confining plasma. After a brief historical overview, the review is divided into two separate but not independent parts: the first illustrates the observational framework, the second reviews the theoretical knowledge. Quiescent loops and their confined plasma are considered and, therefore, topics such as loop oscillations and flaring loops (except for non-solar ones, which provide information on stellar loops) are not specifically addressed here. The observational section discusses the classification, populations, and the morphology of coronal loops, its relationship with the magnetic field, and the loop stranded structure. The section continues with the thermal properties and diagnostics of the loop plasma, according to the classification into hot, warm, and cool loops. Then, temporal analyses of loops and the observations of plasma dynamics, hot and cool flows, and waves are illustrated. In the modeling section, some basics of loop physics are provided, supplying fundamental scaling laws and timescales, a useful tool for consultation. The concept of loop modeling is introduced and models are divided into those treating loops as monolithic and static, and those resolving loops into thin and dynamic strands. More specific discussions address modeling the loop fine structure and the plasma flowing along the loops. Special attention is devoted to the question of loop heating, with separate discussion of wave (AC) and impulsive (DC) heating. Large-scale models including atmosphere boxes and the magnetic field are also discussed. Finally, a brief discussion about stellar coronal loops is followed by highlights and open questions.

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“…Short loops have been studied theoretically (e.g. Müller et al 2003;Sasso et al 2012), indicating that such short hot structures are reasonable, even though these short model loops show peak temperatures of well below 1 MK. Klimchuk et al (1987) found that hot short loops with heights below 1000 km are thermally unstable and evolve into cool loops with temperatures around 10 5 K. This would apply to the miniature loops proposed here, which would not be stable, anyway, because they can be expected to be disturbed rapidly by the convective motions of the granulation.…”

Section: Miniature Coronal Loops In Plage Regionmentioning

confidence: 99%

Structure of solar coronal loops: from miniature to large-scale

Peter

Bingert

Klimchuk

et al. 2013

A&A

121

127

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Aims. We use new data from the High-resolution Coronal Imager (Hi-C) with its unprecedented spatial resolution of the solar corona to investigate the structure of coronal loops down to 0.2 . Methods. During a rocket flight, Hi-C provided images of the solar corona in a wavelength band around 193 Å that is dominated by emission from Fe  showing plasma at temperatures around 1.5 MK. We analyze part of the Hi-C field-of-view to study the smallest coronal loops observed so far and search for the possible substructuring of larger loops. Results. We find tiny 1.5 MK loop-like structures that we interpret as miniature coronal loops. Their coronal segments above the chromosphere have a length of only about 1 Mm and a thickness of less than 200 km. They could be interpreted as the coronal signature of small flux tubes breaking through the photosphere with a footpoint distance corresponding to the diameter of a cell of granulation. We find that loops that are longer than 50 Mm have diameters of about 2 or 1.5 Mm, which is consistent with previous observations. However, Hi-C really resolves these loops with some 20 pixels across the loop. Even at this greatly improved spatial resolution, the large loops seem to have no visible substructure. Instead they show a smooth variation in cross-section. Conclusions. That the large coronal loops do not show a substructure on the spatial scale of 0.1 per pixel implies that either the densities and temperatures are smoothly varying across these loops or it places an upper limit on the diameter of the strands the loops might be composed of. We estimate that strands that compose the 2 thick loop would have to be thinner than 15 km. The miniature loops we find for the first time pose a challenge to be properly understood through modeling.

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Solar low-lying cool loops and their contribution to the transition region EUV output

Cited by 11 publications

References 47 publications

Miniature loops in the solar corona

Miniature loops in the solar corona

Coronal Loops: Observations and Modeling of Confined Plasma

Structure of solar coronal loops: from miniature to large-scale

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