Solar flares: recent advances on observations and modelling
Simulations and Observations of Balmer and Paschen Emission in Flare Onset using Radiative-Hydrodynamic Simulations and data from the Swedish 1-m Solar Telescope
Malcolm Druett
Valentina Zharkova (Northumbria University), Eamon Scullion (Northumbria University)
Northumbria University
Heinzel and Kleint (2014) reported Balmer continuum enhancement in the X1 flare SOL2014-03-29T17:48 using IRIS to inspect the UV. They conclude that this emission is consistent with recombination to hydrogen of the ambient electrons produced by a non-thermal electron beam. Kleint et al. (2016) demonstrate that this continuous emission is much higher than the photospheric blackbody radiation, thus requiring a contribution from the chromospheric radiation.
In this work, hydrodynamic and radiative conditions of hydrogen during flare onset are investigated using a 1-D, fully Non-LTE code built on the work of Zharkova and Kobylinskii (1993) and the hydrodynamic models of Zharkova and Zharkova (2007). Chromospheric continuum enhancements are produced from this NLTE model. Balmer and Paschen emission is evaluated in the near UV, visible, and Near IR. Results are compared to the results of Kleint et al. as well as high-resolution observations (43 km per pixel) from the Swedish 1-metre Solar Telescope (SST) CRISP with pre-filters for Balmer lines for a C1.8 flare event on 1st July 2012. Results provide physical insight into fluctuations in atmospheric depth of Balmer and Paschen line cores and the conditions under which Balmer and Paschen lines become optically thick. Line profiles are used to characterise the hydrodynamic response and the propagation of hydrodynamic shocks passing through the chromosphere. Continuum head and line wing intensities are found to be strongly linked to the beam parameters. This allows us to provide a plausible explanation of the origin of Balmer and Pashen continuum enhancement during white light flares.


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