The Effects of Turbulent Electrical Resistivity on the Response of the Solar Atmosphere to Flare Energy Input. I. Results of Radiative Hydrodynamic Simulations

Abstract

A number of works have considered the role of turbulence in energy release and transport in solar flares, and in particular, on the transport of energy by thermal conduction. Here, we point out that for physical consistency, the effects of turbulence on the electrical conductivity, and hence on the ohmic heating by the return current that neutralizes the current in injected electron beams, must also be considered. Using radiative hydrodynamic simulations, in conjunction with thermal and electrical conductivities modified from their collisional values by turbulent processes, we model the heating rate along a flare loop. We derive the resulting temperature, pressure, velocity, and density profiles, and use them to calculate quantities such as the differential emission measure (DEM) and the emitted X-ray spectrum. For high levels of turbulence, the combination of high electrical resistivity and low thermal conductivity acts to create and sustain a region of very large temperature near the loop apex, creating a large overpressure that acts to suppress the upward evaporation of chromospheric material. Further, the associated large temperature gradients result in a reduction of the DEM at temperatures from 105 K to 107 K. The hard X-ray spectrum at high energies is reduced due to a lower electron flux reaching the chromosphere, but at low energies, it is enhanced due to thermal emission from the very hot coronal plasma. We assess the extent to which these results can be used to constrain the nature and role of turbulent motions in the flare volume.