The Role of Nonlocal Thermal Transport in Flare-driven Chromospheric Evaporation

Abstract Thermal conduction plays an important role in energy transport during solar flares. Flares heat the solar atmosphere to tens of megakelvins, which, combined with mean free paths in excess of 1 Mm, can cause the heat flux to become nonlocal. We use the magnetohydrodynamic Lare2d code to simulate a reconnective heating event with three different thermal conduction models: classical Spitzer–Härm (SH) along the magnetic field, local transport with a heat flux limiter (FL), and the nonlocal Schurtz–Nicolaï–Busquet (SNB) model that is routinely used in laser-plasma codes and has been benchmarked against a full Vlasov–Fokker–Planck treatment. The evolution of the atmosphere post heating is compared between simulations using each of these models. Due to a suppressed heat flux, SNB gives rise to significantly higher peak temperatures than SH. Further, with SNB transport chromospheric evaporation occurs later and has stronger extreme-ultraviolet (EUV) emission intensity. FL simulations have similar temperature evolution and chromospheric evaporation to SNB, however different values of the flux limiter work best for peak temperature, downflow velocity, and EUV emission intensity, and so there is no one optimal value for all cases. We conclude that the SNB model provides a practicable solution to incorporate nonlocal thermal transport at MHD scales, which will be crucial to improve the realism and accuracy of the next generation of solar flare simulations.