The Role of Turbulence for Heating Plasmas in Eruptive Solar Flares

• Published in: The Astrophysical journal Vol. 897; no. 1; pp. 64 - 77
• Main Authors: Ye, Jing, Cai, Qiangwei, Shen, Chengcai, Raymond, John C., Lin, Jun, Roussev, Ilia. I., Mei, Zhixing
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01-07-2020; IOP Publishing
• Subjects: Astrophysics; Computational fluid dynamics; Computer simulation; Conduction; Conduction cooling; Current sheets; Fluid flow; Heating; Light curve; Magnetohydrodynamic turbulence; Magnetohydrodynamical simulations; Plasmas (physics); Radiation; Radiative cooling; Solar activity; Solar atmosphere; Solar flares; Solar magnetic reconnection; Solar observatories; Termination shock; Turbulence; Wavelengths
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ab93b5

Magnetohydrodynamic turbulence is ubiquitous in the process of solar eruptions, and it is crucial for the fast release of energy and the formation of complex thermal structures that have been found in observations. In this paper, we focus on the turbulence in two specific regions: inside the current sheet (CS) and above the flare loops, considering the standard flare model. The gravitationally stratified solar atmosphere is used in MHD simulations, which include the Lundquist number of S = 106, thermal conduction, and radiative cooling. The numerical results are generally consistent with previous simulation work, especially the thermal structures and reconnection rate in flare phases. We can observe the formation of multiple termination shocks (TSs) as well as plasmoid collisions, which make the region above the loop-top more turbulent and heat plasmas to the higher temperature. The spectrum studies show that the property of the MHD turbulence inside the CS is anisotropic, while it is quasi-isotropic above the loop-top. The magnetic spectrum becomes softer when the plasmoids interact with the multiple TSs. Meanwhile, synthetic images and light curves of the Solar Dynamics Observatory/Atmospheric Imaging Assembly 94, 131, 171, 304, and 193 channels show intermittent radiation enhancement by turbulence above the loop-top. The spectrum study of the radiation intensity in these five wavelengths gives quite different power indices at the same time. In particular, quasiperiodic pulsations (QPPs) in the turbulent region above the loop-top are investigated, and we also confirm that the heating for plasmas via turbulence is an important contributor to the source of QPPs.