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<p>On October 3rd, 2024, the Sun emitted an X9.0-class flare from active region NOAA 13842. The event was recorded by multiple space-based instruments, beginning hours before the eruption, granting a unique opportunity to provide insight into the flare’s pre-flare phase. In this study, we employ analysis of Interface Region Imaging Spectrograph (IRIS) spectroscopic data to investigate pre-flaring phenomena associated with this flare. We present time-series and wavelet analysis of non-thermal velocity, Doppler velocity, and line intensity quantities of the IRIS Si IV 1403&#xa0;Å line. We find two ranges of periodic oscillations during the pre-flare phase: ∼ 7 – 10&#xa0;min and ∼ 18 – 21&#xa0;min oscillations, with local enhancements occurring near the polarity inversion line. We also find a steady rise in Si IV line parameters beginning 3 hours before the flare in the same region, transitioning into strong non-thermal velocities and blueshifts <InlineEquation ID="IEq1"> <EquationSource Format="MATHML"><math> <mo>∼</mo> <mspace width="0.2em" /> <mn>15</mn> </math></EquationSource> <EquationSource Format="TEX">${\sim}\,15$</EquationSource> </InlineEquation> minutes before onset. These findings are consistent with a slow destabilization of the coronal magnetic field, possibly driven by the gradual activation of a flux rope, followed by a rapid shift to intense reconnection activity leading to flare onset.</p>

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Investigating Pre-Flare Signatures in Spectroscopic Observations of an X9-Class Solar Flare

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年5月27日

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  • Louis Seyfritz,
  • Maria Kazachenko,
  • Ryan French

摘要

On October 3rd, 2024, the Sun emitted an X9.0-class flare from active region NOAA 13842. The event was recorded by multiple space-based instruments, beginning hours before the eruption, granting a unique opportunity to provide insight into the flare’s pre-flare phase. In this study, we employ analysis of Interface Region Imaging Spectrograph (IRIS) spectroscopic data to investigate pre-flaring phenomena associated with this flare. We present time-series and wavelet analysis of non-thermal velocity, Doppler velocity, and line intensity quantities of the IRIS Si IV 1403 Å line. We find two ranges of periodic oscillations during the pre-flare phase: ∼ 7 – 10 min and ∼ 18 – 21 min oscillations, with local enhancements occurring near the polarity inversion line. We also find a steady rise in Si IV line parameters beginning 3 hours before the flare in the same region, transitioning into strong non-thermal velocities and blueshifts ∼ 15 ${\sim}\,15$ minutes before onset. These findings are consistent with a slow destabilization of the coronal magnetic field, possibly driven by the gradual activation of a flux rope, followed by a rapid shift to intense reconnection activity leading to flare onset.