A Two-dimensional Magnetohydrodynamic Simulation of Chromospheric Evaporation in a Solar Flare Based on a Magnetic Reconnection Model

A two-dimensional simulation of a solar flare is performed using a newly developed magnetohydrodynamic (MHD) code that includes a nonlinear anisotropic heat conduction effect. The numerical simulation starts with a vertical current sheet that is line-tied at one end to a dense chromosphere. The flare energy is released by the magnetic reconnection mechanism that is stimulated initially by the resistivity perturbation in the corona. The released thermal energy is transported into the chromosphere by heat conduction and drives chromospheric evaporation. Owing to the heat conduction effect, the adiabatic slow-mode MHD shocks emanated from the neutral point are dissociated into conduction fronts and isothermal slow-mode shocks. We discovered two new features, i.e., (1) a pair of high-density humps on the evaporated plasma loops that are formed at the collision site between the reconnection flow and the evaporation flow, and (2) a loop-top dense blob behind the fast-mode MHD shock. We also derived a simple scaling law for the flare temperature described as where T_A, B, ρ, and κ₀ are the temperature at the flare loop apex, the coronal magnetic field strength, the coronal density, and the heat conduction coefficient, respectively. This formula is confirmed by the numerical simulations. Temperature and derived soft X-ray distributions are similar to the cusplike structure of long-duration-event (LDE) flares observed by the soft X-ray telescope aboard Yohkoh. Density and radio free-free intensity maps show a simple loop configuration that is consistent with the observation with the Nobeyama Radio Heliograph.