Solar Flare Heating with Turbulent Suppression of Thermal Conduction
Open Access
- 1 May 2022
- journal article
- research article
- Published by American Astronomical Society in The Astrophysical Journal
- Vol. 931 (1), 60
- https://doi.org/10.3847/1538-4357/ac69e8
Abstract
During solar flares, plasma is typically heated to very high temperatures, and the resulting redistribution of energy via thermal conduction is a primary mechanism transporting energy throughout the flaring solar atmosphere. The thermal flux is usually modeled using Spitzer’s theory, which is based on local Coulomb collisions between the electrons carrying the thermal flux and those in the background. However, often during flares, temperature gradients become sufficiently steep that the collisional mean free path exceeds the temperature-gradient scale size, so that thermal conduction becomes inherently nonlocal. Further, turbulent angular scattering, which is detectable in nonthermal widths of atomic emission lines, can also act to increase the collision frequency and thus suppress the heat flux. Recent work by Emslie & Bian extended Spitzer’s theory of thermal conduction to account for both nonlocality and turbulent suppression. We have implemented their theoretical expression for the heat flux (which is a convolution of the Spitzer flux with a kernel function) into the RADYN flare-modeling code and performed a parameter study to understand how the resulting changes in thermal conduction affect the flare dynamics and hence the radiation produced. We find that models with reduced heat fluxes predict slower bulk flows, less intense line emission, and longer cooling times. By comparing the features of atomic emission lines predicted by the models with Doppler velocities and nonthermal line widths deduced from a particular flare observation, we find that models with suppression factors between 0.3 and 0.5 relative to the Spitzer value best reproduce the observed Doppler velocities across emission lines forming over a wide range of temperatures. Interestingly, the model that best matches the observed nonthermal line widths has a kappa-type velocity distribution function.Funding Information
- NASA (80NSSC21K0460)
- NASA (80NSSC21M0362)
This publication has 48 references indexed in Scilit:
- VELOCITY CHARACTERISTICS OF EVAPORATED PLASMA USINGHINODE/EUV IMAGING SPECTROMETERThe Astrophysical Journal, 2009
- CORONAL NONTHERMAL VELOCITY FOLLOWING HELICITY INJECTION BEFORE AN X-CLASS FLAREThe Astrophysical Journal, 2009
- Relaxation of the distribution function tails for systems described by Fokker-Planck equationsPhysical Review E, 2005
- Radiative Hydrodynamic Models of the Optical and Ultraviolet Emission from Solar FlaresThe Astrophysical Journal, 2005
- Mass Motions and Plasma Properties in the 107K Flare Solar CoronaThe Astrophysical Journal, 2003
- Dynamic Models of Optical Emission in Impulsive Solar FlaresThe Astrophysical Journal, 1999
- Does a nonmagnetic solar chromosphere exist?The Astrophysical Journal, 1995
- Non-LTE radiating acoustic shocks and CA II K2V bright pointsThe Astrophysical Journal, 1992
- Transport phenomena in a completely ionized gas with large temperature gradientsPhysical Review A, 1984
- Electron and Ion Runaway in a Fully Ionized Gas. IPhysical Review B, 1959