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Observational Analysis of Lyman α Emission in Equivalent Magnitude Solar Flares View all abstracts by submitter

Harry Joseph Greatorex   Submitted: 2023-06-30 09:12

The chromospheric Lyman α line of neutral hydrogen (Lyα; 1216 ) is the most intense emission line in the solar spectrum, yet until recently observations of flare-related Lyα emission have been scarce. Here, we examine the relationship between nonthermal electrons accelerated during the impulsive phase of three M3 flares that were co-observed by RHESSI, GOES, and SDO, and the corresponding response of the chromosphere in Lyα. Despite having identical X-ray magnitudes, these flares show significantly 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%. By comparing the properties of the nonthermal electrons derived from spectral analysis of hard X-ray observations, flares with a harder spectral index were found to produce a greater Lyα enhancement. 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 ) 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. These results may have implications for space weather studies and modelling the response of the terrestrial atmosphere to changes in the solar irradiance, and will guide the interpretation of flare-related Lyα observations that will become available during Solar Cycle 25.

Authors: Harry J. Greatorex, Ryan O. Milligan, Phillip C. Chamberlin

Publication Status: ApJ (submitted)
Last Modified: 2023-07-05 06:42
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