Dynamical and Thermal Manifestations of the Region above the Top of the Post-flare Loops: MHD Simulations

Observations proved that a distributed structure named a supra-arcade fan (SAF) exists above post-flare loops in solar eruptions. The locations of the SAF are spatially consistent with various emission sources. Termination shocks (TSs) that are often regarded as an efficient driver for particle acceleration possibly exist in the SAF. We performed the numerical simulations of solar flares based on the standard flare model to study the dynamical and thermal manifestations of the SAF, as well as the possibility of detecting TSs in extreme-ultraviolet (EUV) images. In the simulations, the SAF and TSs can be clearly identified. The motion history and temperature evolution of plasmas inside the SAF indicate that the mass of the SAF comes from the corona and the plasmas are heated in the current sheet. The height of the SAF decreases with the speed of about 64.6 km s-1 when the rate of magnetic reconnection quickly increases, and then increases with a slightly lower velocity of about 50.5 km s-1 after the peak of the rate of magnetic reconnection. The descent-ascent path of the SAF is due to the unbalance of the Lorentz force and the pressure force inside the magnetic loops. In synthetic EUV images, emission intensity variations in the area surrounding TSs are significant, indicating that, depending on the viewing angle, TSs could be identifiable in EUV observations. The results of numerical simulations are generally consistent with observations, helping us to better understand the characteristics of the SAF and the physical natures behind it.