Joseph Plowman

Solar plasma composition differs between the photosphere and corona over a range of timescales, with preferential enhancement of elements with low first ionization potential (FIP). However, the physical origin of the FIP fractionation remains incompletely understood. Furthermore, during flares, the FIP bias also exhibits rapid changes, associated with fast transport of material with different FIP biases. We present novel observations from the Solar Orbiter SPICE and Extreme Ultraviolet Imager (EUI), Hinode Extreme Ultraviolet Imaging Spectrometer (EIS), and Chandrayaan-2 Solar X-ray Monitor (XSM) instruments, finding rapid abundance changes in the emitting plasma, on timescales of minutes, during the eruptive M7.6-class solar flare observed on 2024 September 30. These instruments have wide temperature coverage and find contrasting abundance evolution patterns between the hotter and cooler plasma components. 3D reconstruction of the active region and additional observations from the Solar Orbiter STIX X-ray telescope show how the hot and cool plasma components, emitting in different spectral regions and observed with the various instruments, sample the plasma composition evolution in distinct locations within the observed flaring plasma. The bright postflare looptops observed by SPICE show coronal FIP bias, while the hot plasma observed with XSM exhibits FIP bias decreasing from coronal to photospheric during the impulsive phase. We interpret these observations as evidence of the X-ray diagnostics seeing hot coronal reconnection outflows mixing with chromospheric plasma as flare loops sequentially energize and relax, explaining why the FIP bias decreases from coronal to a hybrid; and the cool looptops seen with SPICE show coronal abundances due to coronal material deposited near the looptops.

This paper presents a follow-up to previous work on correcting point-spread-function (PSF)-induced Doppler artifacts in observations by the SPICE spectrograph on Solar Orbiter. In a previous paper, we demonstrated the correction of these artifacts in the y − λ plane with PSF regularization, treating the forward problem with a method based on large sparse matrix inversion. It has since been found that similar apparent artifacts are also present in the x − λ direction, i.e., across adjacent slit positions. Correcting this is difficult (although not impossible) with the previous matrix inversion method due to the time variation between slit positions. We have therefore devised a new method that addresses both x − λ and y − λ artifacts simultaneously by applying wavelength-dependent shifts at each x − y plane of the spectral cube. This paper demonstrates the SPICE data issue, describes the new method, and shows a comparison with the previous one. We explore the time variation of the correction parameters for the SPICE data and show a clear orbit dependence. The results of the method are significantly higher-quality Doppler signals, which we estimate at less than ∼5 km/s uncertainty for brighter lines in the absence of other systematics. Furthermore, we show the new SPICE polar observation results as a demonstration. The correction codes are written in Python, publicly available on GitHub, and can be directly applied to SPICE level 2 datasets.

Aims. We investigate the time evolution of relative elemental abundances in the context of the first ionization potential effect focusing on an active region (AR). Our aim is to characterize this evolution in different types of AR structures as well as in different atmospheric layers. We wish to assess how the measured changes relate to different magnetic topologies by computing abundance enhancement in different conditions using the ponderomotive force model. Methods. Leveraging SPICE (Spectral Imaging of the Coronal Environment) spectroscopic observations of extreme ultraviolet lines from ions formed across a broad temperature range – from the upper chromosphere to the low corona –, we performed relative abundance ratios following differential emission measure analysis. This methodology yields abundance maps from low, intermediate, and high first ionization potential elements. Results. We obtained the temporal evolution of a number of abundance ratios for different structures on the Sun. We compared these results with the outcomes of the ponderomotive force model. We find good correlation between the model and our results, suggesting an Alfvén-wave driven fractionation of the plasma. Fan loops, loop footpoints and AR boundaries exhibit coronal abundances, while the AR core shows more photospheric-like composition. A slow and steady increase in the Mg/Ne first ionization potential bias values is observed, starting around 1.5 and increasing by about 50% after two days. The S/O evolution coupled with the model provides evidence of resonant waves fractionating the plasma in transition region structures.

We present an extension of the Coronal Reconstruction Onto B-Aligned Regions (CROBAR) method to Linear Force Free Field (LFFF) extrapolations, and apply it to the reconstruction of a set of Atmospheric Imaging Assembly, Michelson Doppler Imager, and STEREO EUVI data. The results demonstrate that CROBAR is not only capable of reconstructing coronal emission structures, but also the previously made claim that it can constrain coronal field extrapolations, in this case the LFFF’s α parameter. They also provide a real-world example of how CROBAR can easily incorporate information from multiple perspectives to improve its reconstructions, and we also use the additional perspectives to help validate the reconstructions. We furthermore touch on the use of real-world emission passbands rather than idealized power-law type ones using differential emission measures (DEMs). We conclude with a comparison of CROBAR-generated emission to observed emission and those produced with idealized DEM based power laws. These results further illustrate the promise of CROBAR for real-world applications, and we make available a preliminary release of the software available for download.

Solar flares release a tremendous amount of magnetic energy that subsequently manifests in several forms; the bulk of this energy is transported through the Sun’s atmosphere and explosively heats the chromosphere. While hard X-ray observations have pointed to flare-accelerated electrons as a primary means by which energy is transported following flares, alternative processes undoubtedly act alongside, or even instead of, those energetic electrons. To shed light on this we analysed flare-optimized, high-cadence Solar Orbiter observations. Footpoints from two flare ribbons were observed by the Spectral Imaging of the Coronal Environment (SPICE) instrument. Curiously, those footpoints exhibited contrasting behaviour: one had short-lived yet strong decreases in the Lyman β/Lyman γ line intensity ratio, whereas the other exhibited a more prolonged, moderate dip in that ratio. These observations were compared to synthetic spectra from radiation hydrodynamic simulations of flares driven by various energy transport mechanisms. This revealed that one footpoint was driven by energetic particle precipitation, while the other was driven by enhanced thermal heat flux. The implication is that energetic particles do not dominate along the entirety of flare ribbons. Critically, we must now focus on understanding where, when and why different mechanisms dominate in solar flare energy transport.

Whitepaper #049 in the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033. Main topics: basic research. Additional topics: solar physics.

Whitepaper #048 in the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033. Main topics: basic research. Additional topics: solar physics; space-based missions/projects.