Defining the Middle Corona

West, Matthew J.; Seaton, Daniel B.; Wexler, David B.; Raymond, J. C.; Zanna, G. Del; Kobelski, Adam; Bin, Chen; DeForest, C. E.; Golub, L.; Caspi, Amir; Gilly, Chris R.; Kooi, Jason E.; Meyer, Karen; Alterman, B. L.; Alzate, Nathalia; Andretta, V.; Auchère, F.; Banerjee, D.; Berghmans, D.; Chamberlin, Phillip C.; Chitta, L. P.; Downs, Cooper; Giordano, S.; Harra, L. K.; Higginson, A. K.; Howard, R. A.; Kumar, Pankaj; Mason, Emily; Mason, James Paul; Morton, R. J.; Nykyri, K.; Patel, Ritesh; Rachmeler, Laurel; Reardon, K.; Reeves, Katharine K.; Savage, Sabrina; Thompson, B. J.; Kooten, Samuel J. Van; Viall, N. M.; Vourlidas, A.; Zhukov, A. N.

doi:10.1007/s11207-023-02170-1

Cited by 17 publications

(7 citation statements)

References 312 publications

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“…The filamentary structure is near-radially oriented, which would suggest that it is following the background magnetic field, and extends outward toward the edge of the AIA field of view. This fine structure likely extends into the middle corona (West et al 2023). Enhanced white light images from eclipse observations (Druckmüller et al 2014) appear to confirm this, revealing filamentary structure in polar regions.…”

Section: Discussionmentioning

confidence: 67%

The Fine-scale Structure of Polar Coronal Holes

Morton,

Cunningham

2023

ApJ

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Coronal holes are thought to be composed of relatively broad columnar structures known as plumes. Here, we demonstrate that the plumes (and interplumes) in polar coronal holes are composed of fine-scale filamentary structure, with average scales of 2″–10″. The fine structure is the off-limb analog of the previously found “plumelets” of Uritsky et al. The off-limb observations enable an examination of the fine structure without the influence of the underlying atmosphere along the line of sight. Hence, we show that the fine-scale structure is present at least until the edge of the field of view of the Solar Dynamics Observatory. The fine structure is found to have spatial distribution that follows a k −1 power law perpendicular to the inferred magnetic field direction. For a small sample of the fine structure, the cross-sectional profiles are measured as a function of height. In some cases, the measurements indicate that the fine structure expands super-radially, consistent with existing models of polar field expansion and the expansion of the plumes. We discuss the implications of the presence of the fine structure with respect to understanding wave propagation in the coronal holes and their contribution to powering the solar wind.

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Section: Discussionmentioning

confidence: 67%

The Fine-scale Structure of Polar Coronal Holes

Morton,

Cunningham

2023

ApJ

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“…The middle corona, defined by heliocentric distances from 1.5 to 6 solar radii (R e ), has a tenuous plasma environment where the density is too low for X-ray and EUV emission diagnostics (see West et al 2023). The low-frequency U-bursts, observed by ground-based radio interferometers below 100 MHz, are generated by electron beams traveling along large-sized coronal loops that extend into the middle corona, higher than 1.5 R e heliocentric height.…”

Section: Introductionmentioning

confidence: 99%

Imaging a Large Coronal Loop Using Type U Solar Radio Burst Interferometry

Zhang,

Reid,

Carley

et al. 2024

ApJ

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Solar radio U-bursts are generated by electron beams traveling along closed magnetic loops in the solar corona. Low-frequency (<100 MHz) U-bursts serve as powerful diagnostic tools for studying large-sized coronal loops that extend into the middle corona. However, the positive frequency drift component (descending leg) of U-bursts has received less attention in previous studies, as the descending radio flux is weak. In this study, we utilized LOFAR interferometric solar imaging data from a U-burst that has a significant descending leg component, observed between 10 and 90 MHz on 2020 June 5th. By analyzing the radio source centroid positions, we determined the beam velocities and physical parameters of a large coronal magnetic loop that reached just about 1.3 R ⊙ in altitude. At this altitude, we found the plasma temperature to be around 1.1 MK, the plasma pressure around 0.20 mdyn, cm−2, and the minimum magnetic field strength around 0.07 G. The similarity in physical properties determined from the image suggests a symmetric loop. The average electron beam velocity on the ascending leg was found to be 0.21c, while it was 0.14c on the descending leg. This apparent deceleration is attributed to a decrease in the range of electron energies that resonate with Langmuir waves, likely due to the positive background plasma density gradient along the downward loop leg.

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“…Figure 1 shows typical sky brightness curves under various conditions. During an annular solar eclipse, or at exceptionally high altitude in the atmosphere (e.g., above 80,000 ft. altitude), sky brightness can be reduced by an order of magnitude or more compared to high desert conditions; in turn, that may enable imaging of the middle corona (West et al, 2023) at or above 3 R ⊙ from the Sun without flying an instrument into space or requiring a total solar eclipse. This insight led us to consider new instrument designs that might enable ground-based imaging of the middle corona, farther from the Sun than is possible from the ground under normal conditions.…”

Section: Introductionmentioning

confidence: 99%

CATEcor: an Open Science, Shaded-Truss, Externally Occulted Coronagraph

DeForest,

Seaton,

Caspi

et al. 2024

Preprint

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We present the design of a portable coronagraph, CATEcor, that incorporates a novel “shaded truss” style of external occultation and serves as a proof-of-concept for that family of coronagraphs. The shaded truss design style has the potential for broad application in various scientific settings. We conceived CATEcor itself as a simple instrument to observe the corona during the darker skies available during a partial solar eclipse, or for students or interested amateurs to detect the corona under ideal non-eclipsed conditions. CATEcor is therefore optimized for simplicity and accessibility to the public. It is implemented using an existing dioptric telescope and an adapter rig that mounts in front of the objective lens, restricting the telescope aperture and providing external occultation. The adapter rig, including occulter, is fabricated using fusion deposition modeling (FDM; colloquially “3D printing”), greatly reducing cost. The structure is designed to be integrated with moderate care and may be replicated in a university or amateur setting. While CATEcor is a simple demonstration unit, the design concept, process, and trades are useful for other more sophisticated coronagraphs in the same general family, which might operate under normal daytime skies outside the annular-eclipse conditions used for CATEcor.

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Defining the Middle Corona

Cited by 17 publications

References 312 publications

The Fine-scale Structure of Polar Coronal Holes

The Fine-scale Structure of Polar Coronal Holes

Imaging a Large Coronal Loop Using Type U Solar Radio Burst Interferometry

CATEcor: an Open Science, Shaded-Truss, Externally Occulted Coronagraph

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