Abstract
Abstract The hydrogen Balmer series is a basic radiative loss channel from the flaring solar chromosphere. We report here on the analysis of an extremely rare set of simultaneous observations of a solar flare in the H α and H β lines, at high spatial and temporal resolutions, that were acquired at the Dunn Solar Telescope. Images of the C3.3 flare (SOL2014-04-22T15:22) made at various wavelengths along the H α line profile by the Interferometric Bidimensional Spectrometer (IBIS) and in the H β with the Rapid Oscillations in the Solar Atmosphere (ROSA) broadband imager are analyzed to obtain the intensity evolution. The H α and H β intensity excesses in three identified flare footpoints are well-correlated in time. We examine the ratio of H α to H β flare excess, which was proposed by previous authors as a possible diagnostic of the level of electron-beam energy input. In the stronger footpoints, the typical value of the the H α /H β intensity ratio observed is ∼0.4–0.5, in broad agreement with values obtained from a RADYN non-LTE simulation driven by an electron beam with parameters constrained (as far as possible) by observation. The weaker footpoint has a larger H α /H β ratio, again consistent with a RADYN simulation, but with a smaller energy flux. The H α line profiles observed have a less prominent central reversal than is predicted by the RADYN results, but can be brought into agreement if the H α -emitting material has a filling factor of around 0.2–0.3.
Highlights
Solar flares are explosive phenomena occurring in the solar atmosphere that indicate a rapid conversion of magnetic energy into other forms of energy
We study the flare SOL2014-04-22, which occurred close to the western limb of the Sun, and compare observational data acquired from ground-based and satellite instruments with the results obtained from the Radiative hydrodynamic (RADYN) code (Carlsson & Stein 1997, and Allred et al 2005, 2015) in order to investigate the behavior of Ha and Hb, in response to the energy injected into the chromosphere during flaring
We further investigate the flare event through the comparison between Ha and Hb images acquired by Interferometric Bidimensional Spectrometer (IBIS) and Rapid Oscillations in the Solar Atmosphere (ROSA), respectively
Summary
Solar flares are explosive phenomena occurring in the solar atmosphere that indicate a rapid conversion of magnetic energy into other forms of energy (kinetic, radiative, particle acceleration, etc.). To test and constrain the electron-beam energy transport model, we need to identify sensitive diagnostic radiation signatures, observations of which can be compared to the output of targeted numerical simulations In this regard, the chromosphere presents an ideal test-bed for analyzing the release and redistribution of energy from accelerated particles in this region. Observation and modeling of spectral lines emergent from different layers of the chromosphere can be used to understand how the chromosphere responds to energy input at different heights, and thereby to constrain the beam properties Such investigations serve an additional, exploratory purpose by helping us to identify the best ways—e.g., choices of wavelength, and temporal and spectral resolutions—to get the maximum diagnostic power from flare optical observations, which can be very challenging to plan and execute.
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