The effects of energetic particles on radiative transfer and emission from hydrogen in solar flares

Druett, Malcolm (2017) The effects of energetic particles on radiative transfer and emission from hydrogen in solar flares. Doctoral thesis, Northumbria University.

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Abstract

There are rapid increases of hard and soft X-rays (HXR, SXR) and ultraviolet (UV) emission with large Doppler blue-shifts associated with plasma up-flows observed at flare onsets accompanied by broadened chromospheric emission with large redshifts. H� shows red-shifts of 1–4 Å in the impulsive phase of solar flares observed with various past (Ichimoto and Kurokawa, 1984;Wuelser and Marti, 1989) and current (the Swedish Solar Telescope, SST) instruments (Druett et al., 2017). HXR footpoints are observed to be co-temporal and co-spatial with increases in white light (WL) and continuous emission during the impulsive phase. These effects point to fast, effective sources of excitation and ionisation of hydrogen atoms in flaring atmospheres associated with HXR emission. Most current radiative hydrodynamic models can account for SXR and UV emission, but fail to explain correctly the strongly red-shiftedH� line emission occurring at the flare onsets or the locations of the white light sources, and offer little explanation of the origin of seismic sources in flaring event.

We investigate electron beams as the agents accounting for the observed hydrogen line and continuum emission by considering a 1D hydrodynamic response of the quiet Sun chromosphere to injection of an electron beam and its conversion into a flaring atmosphere with its own kinetic temperatures, densities and macro-velocities (Zharkova and Zharkov, 2007). A radiative response in these atmospheres is simulated using a fully non-local thermodynamic equilibrium (NLTE) approach for a 5 levels plus continuum hydrogen atom model. Simultaneous steady state and integral radiative transfer equations in all optically thick transitions (Lyman and Balmer series) are solved iteratively for all the transitions to define their source functions with the relative accuracy of 10

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