An evaluation of different recipes for chromospheric radiative losses in solar flares

¹ Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, CAS, Nanjing 210023, PR China
² School of Astronomy and Space Science, University of Science and Technology of China, Hefei, 230026, PR China
³ School of Astronomy and Space Science, Nanjing University, Nanjing 210023, PR China
e-mail: jiehong@nju.edu.cn
⁴ Key Laboratory for Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education, Nanjing 210023, PR China

Received: 28 July 2022
Accepted: 8 October 2022

Abstract

Context. Radiative losses are an indispensable part of the numerical simulation of flares. Detailed calculations could be computationally expensive, especially in the chromosphere. There have been some approximate recipes for chromospheric radiative losses in flares, yet their feasibility in flare simulations needs further evaluation.

Aims We aim to evaluate the performance of different recipes for chromospheric radiative losses in flare simulations.

Methods. We compared the atmospheric structure and the line profiles in beam-heated flares calculated with detailed radiative losses and the approximate recipes.

Results. Both the Gan & Fang (1990, ApJ, 358, 328; hereafter GF90) and Hong, J., et al. (2022, A&A, 661, A77) recipes provide acceptable total radiative losses compared with the detailed treatment, but there are discrepancies in the different atmospheric layers during the different evolutionary phases, which lead to misestimations of temperature and line intensity. The recipe of GF90 overestimates the coolings in the upper chromosphere greatly when the temperature exceeds 10⁵ K, which also affects the flare evolution and the line asymmetries. Radiative heating in the middle chromosphere only functions in the initial stage and could be safely neglected. However, radiative heating from the Lyman continuum could dominate near the transition region.