Spectroscopic Observations of Supra-arcade Downflows
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...
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2025-01-01
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| Online Access: | https://doi.org/10.3847/2041-8213/adde59 |
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| author | Ryan J. French Maria D. Kazachenko Teodora Mihailescu Katharine K. Reeves |
| author_facet | Ryan J. French Maria D. Kazachenko Teodora Mihailescu Katharine K. Reeves |
| author_sort | Ryan J. French |
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| description | 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 Fe XXIV 192.02 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 Fe XXIV 255.11 Å and Fe XXIII 263.41 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. |
| format | Article |
| id | doaj-art-9fd80c100ab54c2592237f1aedcf5a85 |
| institution | Kabale University |
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| language | English |
| publishDate | 2025-01-01 |
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| spelling | doaj-art-9fd80c100ab54c2592237f1aedcf5a852025-08-22T17:26:24ZengIOP PublishingThe Astrophysical Journal Letters2041-82052025-01-019861L1610.3847/2041-8213/adde59Spectroscopic Observations of Supra-arcade DownflowsRyan J. French0https://orcid.org/0000-0001-9726-0738Maria D. Kazachenko1https://orcid.org/0000-0001-8975-7605Teodora Mihailescu2https://orcid.org/0000-0001-8055-0472Katharine K. Reeves3https://orcid.org/0000-0002-6903-6832Laboratory for Atmospheric and Space Physics, University of Colorado Boulder , Boulder, CO 80303, USA; National Solar Observatory , 3665 Discovery Drive, Boulder, CO 80303, USALaboratory for Atmospheric and Space Physics, University of Colorado Boulder , Boulder, CO 80303, USA; National Solar Observatory , 3665 Discovery Drive, Boulder, CO 80303, USA; Department of Astrophysical and Planetary Sciences, University of Colorado Boulder , 2000 Colorado Avenue, Boulder, CO 80305, USANASA Goddard Space Flight Center , Greenbelt, MD 20771, USA; Universities Space Research Association , Washington, DC 20024, USAHarvard-Smithsonian Center for Astrophysics , 60 Garden Street, Cambridge, MA 02138, USADespite 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 Fe XXIV 192.02 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 Fe XXIV 255.11 Å and Fe XXIII 263.41 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.https://doi.org/10.3847/2041-8213/adde59Solar flaresSolar extreme ultraviolet emissionSolar flare spectraSolar magnetic reconnectionActive solar coronaSolar physics |
| spellingShingle | Ryan J. French Maria D. Kazachenko Teodora Mihailescu Katharine K. Reeves Spectroscopic Observations of Supra-arcade Downflows The Astrophysical Journal Letters Solar flares Solar extreme ultraviolet emission Solar flare spectra Solar magnetic reconnection Active solar corona Solar physics |
| title | Spectroscopic Observations of Supra-arcade Downflows |
| title_full | Spectroscopic Observations of Supra-arcade Downflows |
| title_fullStr | Spectroscopic Observations of Supra-arcade Downflows |
| title_full_unstemmed | Spectroscopic Observations of Supra-arcade Downflows |
| title_short | Spectroscopic Observations of Supra-arcade Downflows |
| title_sort | spectroscopic observations of supra arcade downflows |
| topic | Solar flares Solar extreme ultraviolet emission Solar flare spectra Solar magnetic reconnection Active solar corona Solar physics |
| url | https://doi.org/10.3847/2041-8213/adde59 |
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