Doppler signature of a possible termination shock in an off-limb solar flare

Ryan J. French, Sijie Yu, Bin Chen, Chengcai Shen, Sarah A. Matthews

Research output: Contribution to journalArticlepeer-review


We report striking Doppler velocity gradients observed during the well-observed 2017 September 10 solar flare, and argue that they are consistent with the presence of an above-the-looptop termination shock beneath the flare current sheet. Observations from the Hinode Extreme-ultraviolet Imaging Spectrometer measure plasma sheet Doppler shifts up to 35 km s−1 during the late-phase of the event. By comparing these line-of-sight flows with plane-of-sky (POS) measurements, we calculate total velocity downflows of 200+ km s−1, orientated ≈6-10 out of the POS. The observed velocities drop rapidly at the base of the hot plasma sheet seen in extreme ultraviolet, consistent with simulated velocity profiles predicted by our 2.5D magnetohydrodynamics model that features a termination shock at the same location. Finally, the striking velocity deceleration aligns spatially with the suppression of Fe XXIV non-thermal velocities, and a 35-50 keV hard X-ray looptop source observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager. Together, these observations are consistent with the presence of a possible termination shock within the X8.2-class solar flare.

Original languageEnglish (US)
Pages (from-to)6836-6844
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Mar 1 2024

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • magnetic reconnection
  • Sun: corona
  • Sun: flares
  • Sun: UV radiation
  • Sun: X-rays, gamma-rays
  • techniques: imaging spectroscopy


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