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Abstract Despite their somewhat frequent appearance in extreme-ultraviolet (EUV) imaging of off-limb flares, the origins of supra-arcade downflows (SADs) remain a mystery. Appearing as dark, tendril-like downflows above growing flare loop arcades, SADs themselves are yet to be tied into the standard model of solar flares. The uncertainty of their origin is, in part, due to a lack of spectral observations, with the last published SAD spectral observations dating back to the Solar and Heliospheric Observatory/Solar Ultraviolet Measurements of Emitted Radiation era in 2003. In this work, we present new observations of SADs within an M-class solar flare on 2022 April 2, observed by the Hinode EUV Imaging Spectrometer (EIS) and the NASA Solar Dynamics Observatory. We measure FeXXIV192.02 Å Doppler downflows and nonthermal velocities in the low-intensity SAD features, exceeding values measured in the surrounding flare fan. The ratio of temperature-sensitive FeXXIV255.11 Å and FeXXIII263.41 Å lines also allows the measurement of electron temperature, revealing temperatures within the range of the surrounding flare fan. We compare EIS line-of-sight Doppler velocities with plane-of-sky velocities measured by Atmospheric Imaging Assembly, to construct the 3D velocity profile of four prominent SADs, finding evidence for their divergence above the flare loop arcade—possibly related to the presence of a high-altitude termination shock. Finally, we detect “stealth” SADs, which produce SAD-like Doppler signals, yet with no change in intensity.
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Demonstration of a portable system for daytime optical turbulence profile measurements
ABSTRACT Measurements of the optical turbulence profile are critical for selecting a potential new solar observational site or for characterizing an existing solar observatory. To measure the turbulence distribution to a moderate altitude above an existing observatory, current techniques use a large facility telescope with an aperture size larger than 1.0 m. This limits their application, especially in surveys to find a new potential site where no large facility telescope is available and where a portable measurement device is needed for such measurements. To address the above issues, we propose a new technique, termed the Advanced Multiple Aperture Seeing Profiler (A-MASP), which uses solar granulation to measure the daytime optical turbulence profile. The A-MASP is a portable system and thus can fully address the fundamental limitation of current optical turbulence profile measurement techniques. The A-MASP consists of two small telescopes, each with an aperture of the order of 100 mm, which can measure the turbulence profile to an altitude up to 20 km. Here, we present our A-MASP development work and its initial on-site measurements at the Big Bear Solar Observatory. In a proof-of-concept experiment, it was successfully demonstrated that the A-MASP can reliably measure the turbulence profile up to 12 km with a vector separation of 0.7 m between the two telescopes. The A-MASP could be used for future surveys to find potentially good observational sites.
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- Award ID(s):
- 1821294
- PAR ID:
- 10377244
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 517
- Issue:
- 3
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 3303-3311
- Size(s):
- p. 3303-3311
- Sponsoring Org:
- National Science Foundation
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