CHLARE · CHromospheric magnetic fields in fLAREs and their evolution

CHromospheric magnetic fields in fLAREs and their evolution

This research project aims to investigate the variations of the solar magnetic field during flares, which are the most energetic events in our solar system. Solar flares play an important role in society due to their ability to temporarily disrupt technology and infrastructure, influence communication systems, and contribute to scientific research and environmental phenomena. Despite the significant impact of flares on modern technology, their timing and location remain unpredictable. Changes in the solar magnetic field topology are recognized as the primary cause of flares, but their underlying physics is not fully understood. Previous studies have demonstrated notable changes in the magnetic field within the photosphere during flares. However, research on the chromosphere, located higher in the atmosphere where flares have their origin, is limited due to the specialized instrumentation required by ground-based telescopes. The He I 1083.0 nm triplet is identified as the most suitable spectral range for studying the upper chromosphere. Objectives Since there are no diagnostic tools available for analyzing the He I triplet in flares, the primary objective is to upgrade an existing tool to interpret spectral profiles of He I in emission, as they occur in flares. The secondary objective is to utilize the enhanced tool to analyze the evolution of the magnetic field vector in existing datasets for the first time. To put the results into context, additional observations will be used. Finally, new observations of flares with Europe’s largest solar telescope GREGOR are planned, as the current amount of spectropolarimetric flare observations using the He I triplet is very limited. Conclusions The HAZEL code, widely utilized in the scientific community, serves as the primary tool for robust spectral-line inversions of the He I triplet. However, it cannot interpret He I profiles in flares. The code was thoroughly upgraded to allow for inversions of the He I triplet in flares. The chromospheric magnetic field was inferred at different stages of an M-class flare, using the upgraded inversion tool. Enhancements of up to 1000 G in the magnetic field strength in the flare are seen in the active part of the flare. The line-of-sight inclination shows significant changes at the borders of the flare. Furthermore, we successfully inverted another chromospheric line, the Ca II 854.2 nm line, which was simultaneously observed alongside the He I triplet. Such combinations of spectral lines in flares are rare, offering significant potential for discovery science. The novel NLTE inversion code DeSIRe was employed to interpret the Ca II flare observations. Our investigation revealed that the Ca II profile, particularly under extreme atmospheric conditions such as flares, can be prone to misinterpretation by inversion codes. Comparison with the He I physical maps resolved ambiguities encountered in the Ca II inversions, highlighting the importance of multi-wavelength studies. The combination of He I and Ca II inversions reveals plasma motions directed upward at the active front of the flare. We underscore the importance of high-cadence chromospheric instrumentation for both, space and ground-based telescopes in comprehending the nature of flares.

Data: CORDIS, © European Union