Radiation Synthesis Tools: Arbitrary Perspective Multiwavelength Radiation Synthesis for Solar Magnetohydrodynamic Simulations

Abstract Solar magnetohydrodynamic (MHD) simulation is an indispensable method for studying solar activities. Modern MHD simulations are increasingly realistic and need to be synthesized with multiwavelength radiation to validate observations. We developed radiation synthesis tools (RST), a Cython-optimized Python program to solve the radiative transfer equation, enabling efficient multiwavelength synthesis of optically thick radiation from arbitrary perspectives. By directly calculating the ray traversal distance ds per cell, RST eliminates interpolation. As a result, the computational complexity in Cartesian coordinates is reduced from O ( N ) (where N = n x · n y · n z is the total number of voxels in the simulation volume) to O ( k · n ) (where k is the number of ray footpoints and n is the number of sampling steps along each ray), significantly improving efficiency, especially for localized high-resolution synthesis. For spherical coordinates, RST offers two methods. The first interpolates data into Cartesian coordinates for fast O ( k · n ) integration, sacrificing small r resolution. And the second computes ray-plane intersections directly, with O ( k · n · log n ) complexity. RST features a user-friendly interface where users simply specify absorption ( κ ) and emissivity ( j ). It includes physical modules for white-light corona, H α , EUV, radio, and pseudo-radiation.