| Presentation Title: | Observational Analysis of Lyman-alpha Emission in Equivalent Magnitude Solar Flares |
| Author(s): | Harry J. Greatorex, Ryan O. Milligan, Phillip C. Chamberlin |
Abstract:
The significant intensity of Lyman-alpha (Lyα; 1216 Ĺ) emission in the solar spectrum makes it a crucial component to our understanding of the energy transport processes in solar flares. Despite this, observations of short-term variability in the Sun's irradiance at Lyα wavelengths have been scarce until relatively recently. Milligan et al. (2020) and Milligan (2021) showed that the energy radiated in Lyα and the corresponding flux enhancement both tend to increase with flare magnitude, respectively. However, we hypothesise that a more fundamental driver may be responsible for the variability in Lyα flux rather than the flare magnitude alone. Here we present observational analysis of three M3 flares that were co-observed by RHESSI, GOES, and SDO, which despite their equivalent magnitudes showed distinctly different Lyα responses. The peak Lyα enhancements above quiescent background for these flares were 1.5%, 3.3%, and 6.4%. However, the predicted Lyα enhancements from FISM2 were consistently <2.5%. Deriving the properties of the nonthermal electrons from HXR spectroscopy, it was found that flares with a ‘harder’ spectral index tended to produce a greater enhancement in Lyα. The percentage of nonthermal energy radiated by the Lyα line during the impulsive phase was found to range from 2.0–7.9%. Comparatively, the radiative losses in He II (304 Ĺ) were found to range from 0.6–1.4% of the nonthermal energy while displaying enhancements above the background of 7.3–10.8%. FISM2 was also found to underestimate the level of He II emission in two out of the three flares. With new generation Lyα instruments onboard present and upcoming missions, the results from this study may guide the interpretation of future Lyα observations of flares in Solar Cycle 25.