DR. ANUSHA BHASARI

To understand the structuring and dynamics of the upper photosphere and the chromosphere of the Sun, we need to improve and extend the existing numerical radiation-magnetohydrodynamical (MHD) simulations. In the solar chromosphere, radiative energy transport is dominated by only the strongest spectral lines. For these lines, the approximation of local thermo-dynamic equilibrium (LTE) is known to be very inaccurate, and a state of equilibrium cannot be assumed in general. To calculate the radiative energy transport under these conditions, the population evolution equation must be evaluated including all time dependent terms. To this end, we have developed a non-LTE non-equilibrium radiative transfer (RT) module to the well-known MHD code MURaM. In this module we have developed a numerical method to solve the evolution equation for the atomic level populations in a time-implicit way, keeping all time dependent terms to first order. Our main non-equilibrium treatment is of the Hydrogen bound and free states. For the equation of state, to determine kinetic temperature, we treat the Hydrogen molecular evolution also in non-equilibrium. The other elements comprising the gas are treated in LTE. Finally, the pressure and the radiative flux divergence from the RT module are provided to the MHD equations, to evolve the MHD and the radiative quantities self-consistently and iteratively. The module is developed for one, two and three dimensions (1d,2d, 3d) but currently tested in 1d. In this talk, the speaker will describe the method, discuss equilibrium solutions and show some results of the dynamic evolution.