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Efficient Calculation of Non-Local Thermodynamic Equilibrium Effects in Multithreaded Hydrodynamic Simulations of Solar Flares View all abstracts by submitter

Jeffrey Reep   Submitted: 2018-06-26 08:45

Understanding the dynamics of the solar chromosphere is crucial to understanding the transport of energy across the atmosphere, especially in impulsive heating events. The chromosphere is optically thick and described by non-local thermodynamic equilibrium (NLTE), often making observations difficult to interpret. There is also considerable evidence that the atmosphere is filamented and that current instruments do not sufficiently resolve small scale features. In flares, for example, it is likely that multithreaded models are required to describe and understand the heating process. The combination of NLTE effects and multithreaded modeling requires computationally demanding calculations, which has motivated the development of a model that can efficiently treat both. We describe the implementation of a solver in a hydrodynamic code for the hydrogen level populations that approximates the NLTE solutions. We derive an accurate electron density across the chromosphere and corona that includes the effects of non-equilibrium ionization for helium and metals. We show the effects of this solver on simulations, which we then use to synthesize light curves and Doppler shifts of spectral lines, with a post-processing radiative transfer code. We demonstrate the utility of this model on multithreaded simulations, where we simulate IRIS observations of a small flare. We show that observed velocities in Mg II, C II, and O I can be explained with a multithreaded model of loops subject to electron beam heating, so long as NLTE effects are treated. The synthesized intensities, however, do not match observed ones very well, which we suggest is primarily due to assumptions about the initial atmosphere. We briefly show how altering the initial atmosphere can drastically alter line profiles and derived quantities, and suggest that it should be tuned to preflare observations for better agreement.

Authors: Jeffrey W. Reep, Stephen J. Bradshaw, Nicholas A. Crump, Harry P. Warren
Projects: None

Publication Status: Submitted to ApJ
Last Modified: 2018-06-26 11:52
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