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The Sun’s dynamic extended corona observed in extreme ultraviolet

Abstract

The ‘middle corona’ is a critical transition between the highly disparate physical regimes of the lower and outer solar coronae. Nonetheless, it remains poorly understood due to the difficulty of observing this faint region (1.5–3 R). New observations from the Solar Ultraviolet Imager of a Geostationary Operational Environmental Satellite in August and September 2018 provide the first comprehensive look at this region’s characteristics and long-term evolution in extreme ultraviolet. Our analysis shows that the dominant emission mechanism here is resonant scattering rather than collisional excitation, consistent with recent model predictions. Our observations highlight that solar wind structures in the heliosphere originate from complex dynamics manifesting in the middle corona that do not occur at lower heights. These data emphasize that low-coronal phenomena can be strongly influenced by inflows from above, not only by photospheric motion, a factor largely overlooked in current models of coronal evolution. This study reveals the full kinematic profile of the initiation of several coronal mass ejections, filling a crucial observational gap that has hindered understanding of the origins of solar eruptions. These new data uniquely demonstrate how extreme ultraviolet observations of the middle corona provide strong new constraints on models seeking to unify the corona and heliosphere.

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Fig. 1: Normalized brightness fall-off as a function of height along a radial cut of ~6° through a streamer.
Fig. 2: Selected composite SUVI images at 171 Å (gold) and 195 Å (blue).
Fig. 3: Selected SUVI 195 Å and white-light LASCO C2 coronagraph composite images.
Fig. 4: Height–time diagrams showing radial evolution of features as a function of time at selected positions, wavelengths and time ranges.

Data availability

Standard SUVI observations are available for download via the NOAA National Centers for Environmental Information (NCEI) GOES-R archive67. Preliminary data products from this campaign, as used in this paper, as well as additional documentation and observations from subsequent campaigns, are available at the same website. Fully processed SUVI observations will be made public as they become available.

Code availability

The data processing and analysis discussed in this paper leveraged publicly available software packages in Python and SolarSoft IDL. The specific processing steps that generated figures and videos presented in this paper used an iterative process that spanned several platforms and multiple languages, and therefore publication of the code in a single, self-contained processing package is not straightforward. However, all processing codes will be provided on request.

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Acknowledgements

We acknowledge our colleagues at the GOES-R Program Office, on the SUVI team at Lockheed Martin, and at NOAA’s National Centers for Environmental Information and Space Weather Prediction Center for providing support and helpful input during the development of this campaign and during the analysis of results, particularly P. C. Sullivan, G. J. Comeyne, M. Shaw-Lecert, R. R. Minor, R. Redmon, J. Machol, L. Rachmeler and S. Hill. D.B.S. and J.M.H. acknowledge support for GOES-R activities at the Cooperative Institute for Research in Environmental Sciences via NOAA cooperative agreement no. NA17OAR4320101, and D.B.S. acknowledges support from NASA grant no. 80NSSC20K1283. A.C. acknowledges funding from NASA grant no. NNX15AQ68G, and A.C. and C.E.D. acknowledge NASA PUNCH contract no. 80GSFC18C0014.

Author information

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Authors

Contributions

D.B.S. led the data analysis, image processing and visualization efforts. J.M.H. developed image processing software. S.K.T. and A.K. developed the campaign and assisted with its implementation, data acquisition and analysis. A.C. and C.E.D. assisted with interpretation of the data and development of data visualizations. N.E.H., R.S. and G.S. developed software for SUVI data calibration and assembly of mosaics and assisted with interpretation of data. D.B.S. and A.C. led the writing of the manuscript, with contributions from the other authors.

Corresponding author

Correspondence to Daniel B. Seaton.

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The authors declare no competing interests.

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Peer review information Nature Astronomy thanks Astrid Veronig and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Table 1 and legends/captions for Supplementary Videos 1–4.

Supplementary Video 1

Composite SUVI movie at 171 Å (gold) and 195 Å (blue). The labelled panels in the corresponding Fig. 2 highlight dynamic features and events that are of particular interest. Timestamps permit the identification of these events within the movie.

Supplementary Video 2

Two-panel rendering of Video 1, at 171 Å (gold) and 195 Å (blue).

Supplementary Video 3

SUVI 195 Å and visible-light LASCO C2 coronagraph composite movie. The labelled panels in the corresponding Fig. 3 highlight dynamic features and events that are of particular interest. Timestamps permit the identification of these events within the movie.

Supplementary Video 4

Uncropped rendering of SUVI 195 Å frames from Video 3. Images are presented in natural SUVI camera coordinates, with celestial north oriented upwards and solar north rotated roughly 20° counterclockwise from vertical.

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Seaton, D.B., Hughes, J.M., Tadikonda, S.K. et al. The Sun’s dynamic extended corona observed in extreme ultraviolet. Nat Astron 5, 1029–1035 (2021). https://doi.org/10.1038/s41550-021-01427-8

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