Beam Electrons as a source of Hα Flare Ribbons

From early 80s the observations of solar flare onsets show rapid increases of hard and soft X-rays, ultra-violet emission with large Doppler blue shifts associated with plasma upflows (with velocities up to 1000 km⋅s-1) and Hα hydrogen emission with red shifts up to 1-4 Å (downward velocities up to 50-200 km⋅s-1). Modern radiative hydrodynamic models account well for blue-shifted emission but struggle to reproduce closely the red-shifted Hα lines. Here we present the first joint hydrodynamic and radiative model showing that during first seconds of beam injection the effects caused by beam electrons can reproduce Hα line profiles with large red-shifts corresponding to a downward velocity of 45-50 km⋅s-1 and matching closely those observed in C1.5 flare with Swedish Solar Telescope. The model also accounts closely for timing and magnitude (93 km⋅s-1) of upward motion to the corona observed 29 s after the event onset in 171 Å by the Atmospheric Imaging Assembly/Solar Dynamics Observatory.