Nonlocal heat flux effects on temperature evolution of the solar atmosphere

Abstract

Context. Heat flux is one of the main energy transport mechanisms in the weakly collisional plasma of the solar corona. There, rare binary collisions let hot electrons travel over long distances and influence other regions along magnetic field lines. Thus, the fully collisional heat flux models might not describe transport well enough since they consider only the local contribution of electrons. The heat flux in weakly collisional plasmas at high temperatures with large mean free paths has to consider the nonlocality of the energy transport in the frame of nonlocal models in order to treat energy balance in the solar atmosphere properly. Aims. We investigate the impact of nonlocal heat flux on the thermal evolution and dynamics of the solar atmosphere by implementing a nonlocal heat flux model in a 3D magnetohydrodynamic simulation of the solar corona. Methods. We simulate the evolution of solar coronal plasma and magnetic fields considering both a local collision dominated and a nonlocal heat flux model. The initial magnetic field is obtained by a potential extrapolation of the observed line-of-sight magnetic field of AR11226. The system is perturbed by moving the plasma at the photosphere. We compared the simulated evolution of the solar atmosphere in its dependence on the heat flux model. Results. The main differences for the average temperature profiles were found in the upper chromosphere/transition region. In the nonlocal heat transport model case, thermal energy is transported more efficiently to the upper chromosphere and lower transition region and leads to an earlier heating of the lower atmosphere. As a consequence, the structure of the solar atmosphere is affected with the nonlocal simulations producing on average a smoother temperature profile and the transition region placed about 500 km higher. Using a nonlocal heat flux also leads to two times higher temperatures in some of the regions in the lower corona. Conclusions. The results of our 3D MHD simulations considering nonlocal heat transport supports the previous results of simpler 1D two-fluid simulations. They demonstrated that it is important to consider a nonlocal formulation for the heat flux when there is a strong energy deposit, like the one observed during flares, in the solar corona.

Models of thermal conduction and non-local transport of relevance to space physics with insights from laser–plasma theory

“…This occurs as the most energetic electrons have the longest mean-free paths, and this effect is not captured by flux limiters. The non-local energy transport models used in solar 1D ( (Karpen and Devore, 1987;West et al, 2004)) and 3D (Silva et al, 2018) models have relied on the kernel model derived for laser-plasmas (Luciani et al, 1983), commonly referred to as the LMV model. In this model, the heat flux is calculated by convolving the local conduction with a non-local kernel.…”

“…Thus, kernel-based models are able to capture the nonlocal effect, but there remain free parameters, such as a in the LMV model, and there is no unique choice of kernel universally proven to be optimal in all conditions. 3D flare simulations (Silva et al, 2018) have included LMV style non-local electron transport in MHD flare models and shown that this significantly changes the predictions for the temperature of the transition region and upper chromosphere.…”

Numerical simulations of macrospicule jets under energy imbalance conditions in the solar atmosphere

“…For instance, in Botha et al (2011) the authors performed numerical simulations and found that thermal conduction plays an essential role in the kink instability of coronal loops. Also, in Silva et al (2018), the authors found that thermal energy is transported more efficiently to the upper chromosphere and lower transition region and led to earlier heating of the lower atmosphere. Additionally, in González-Avilés et al (2017, the authors investigated the importance of magnetic resistivity itself and its relation to the magnetic reconnection process on the formation and evolution of jet with Type II spicules' characteristics.…”