Flare-Driven Plasma Dynamics and Elemental Abundance Redistribution

TL;DR

This work investigates how flare-driven plasma dynamics influence elemental abundances through the solar FIP effect. By combining time-resolved XSM spectroscopy with multi-channel EUV imaging and HYDRAD hydrodynamic modeling, the authors connect energy deposition depth in the chromosphere to element-specific fractionation via evaporation from different heights. They find that the impulsive phase produces a uniform coronal composition, while the decay phase shows element-dependent recovery speeds, with Fe rebounding fastest due to association with the hottest plasma. The results reveal a dynamic coupling between flare energy, upflowing plasma, and abundance variability, offering a framework to interpret cross-layer transport in solar and stellar atmospheres and guiding future abundance-mapping observations.

Abstract

Since the advent of X-ray and EUV spectroscopy, the discovery of the First Ionization Potential (FIP) effect--where coronal elemental compositions diverge from their photospheric values based on the element's FIP--has remained a key puzzle in solar and stellar astrophysics. These deviations exhibit significant fluctuations during flares, yet their connection to plasma dynamics has remained unclear. Here, we report a clear correlation between temperature-sensitive flaring plasma emission and element-specific abundance changes for a solar flare. These findings indicate that energy deposition in the chromosphere drives plasma evaporation from different chromospheric heights, modulating elemental abundances. Hydrodynamic simulations support these observations, showing that varying energy deposition magnitudes generate plasma upflows from different chromospheric heights, leading to element-specific FIP fractionation. These results provide new insights into the dynamic coupling of flare energy, plasma flows, and abundance variability, with implications for understanding coupling between different atmospheric layers.

Figures (5)

• Figure 1: Observations of the flare: Sol2022-09-17T20:40. $|$a, X-ray and EUV light curves of the flare observed by XSM in the 1–8 Å range ( grey), and AIA passbands: 131 Å ( red), 94 Å Fe XVIII ( green), and 211 Å ( blue) respectively. The brown and magenta curves with 1-$\sigma$ errorbars in panel b show the measured temperature from the XSM spectral analysis. Two-temperature represents the two components in spectral fitting. c–e, AIA images at three different times indicated by vertical dashed lines in panel a. White arrows indicate the location of maximum bightenings and the vertical dotted lines in panel c represent the slits for which AIA light-curves are shown in Figure \ref{['fig_abund_evol']}. The X and Y axes are AIA pixel unit.
• Figure 2: XSM Spectra$|$ Green, brown, and blue points with error bars represent the observed XSM spectra at three representative times. Solid lines show the fitted spectra. The gray curve corresponds to the non-solar background spectrum when the Sun was not in the XSM field of view. Lower panel show the residuals.
• Figure 3: Correlation between FIP bias variations and plasma flows$|$ Brown, blue, and orange points with 1-$\sigma$ error-bars represent the variation of the FIP bias for Fe, Si, and S during the flare. Fe FIP bias measurements are available only during periods of intense emission at higher temperatures. The red, green, and cyan filled curves show the normalized flare light curves in the AIA 131 Å, Fe XVIII, and 211 Å passbands, measured along the slits marked in the left panel of Figure \ref{['fig-flarelc']}b. Arrows indicate the plasma flows derived from intensity peaks at each slit: right-facing arrows denote upflows, while left-facing arrows represent downflows. The blue dotted line represents the normalized XSM light curve. The y-axis of all light curve are inverted.
• Figure 4: Simulated coronal loop showing plasma perturbation from different chromospheric heights in response to varying heat deposition.$|$a Time evolution of coronal temperature (solid lines) and density (dashed lines) for three different simulations with maximum volumetric heat deposition rates of 2.0 erg cm$^{-3}$ s$^{-1}$ (red), 1.0 erg cm$^{-3}$ s$^{-1}$ (green), and 0.5 erg cm$^{-3}$ s$^{-1}$ (blue) at the top of the chromosphere. b–d Density perturbations at different chromospheric depths at the time step indicated by the vertical dashed line in panel a, for the three heat deposition cases. The horizontal dashed lines mark the top of the chromosphere. d Variation in FIP fractionation of Fe, Si, and S at different chromospheric depths for a typical closed coronal loop environment due to the ponderomotive force, as estimated by Laming_2019ApJ...879..124L.
• Figure 5A: Location of Flare Sol2022-09-17T20:40$|$a Full-disk AIA 131 Å image of the Sun, highlighting all major activity. The red box indicates the flare location. b AIA 131 Å light curves corresponding to the regions marked in a, color-coded to match the boxes. The gray dashed curve represents the XSM X-ray count rate in the 1–15 keV energy range.