Accelerating NLTE radiative transfer by means of the Forth-and-Back Implicit Lambda Iteration: A two-level atom line formation in 2D Cartesian coordinates

作者：Milic Ivan^*; Atanackovic Olga

来源：Advances in Space Research, 2014, 54(7): 1297-1307.

DOI：10.1016/j.asr.2014.05.025

• Radiative transfer
• Line formation
• Numerical techniques

State-of-the-art methods in multidimensional NLTE radiative transfer are based on the use of local approximate lambda operator within either Jacobi or Gauss-Seidel iterative schemes. Here we propose another approach to the solution of 2D NLTE RT problems, Forth-and-Back Implicit Lambda Iteration (FBILI), developed earlier for 1D geometry. In order to present the method and examine its convergence properties we use the well-known instance of the two-level atom line formation with complete frequency redistribution. In the formal solution of the RT equation we employ short characteristics with two-point algorithm. Using an implicit representation of the source function in the computation of the specific intensities, we compute and store the coefficients of the linear relations J = a + bS between the mean intensity J and the corresponding source function S. The use of iteration factors in the %26apos;local%26apos; coefficients of these implicit relations in two %26apos;inward%26apos; sweeps of 2D grid, along with the update of the source function in other two %26apos;outward%26apos; sweeps leads to four times faster solution than the Jacobi%26apos;s one. Moreover, the update made in all four consecutive sweeps of the grid leads to an acceleration by a factor of 6-7 compared to the Jacobi iterative scheme.

• 出版日期2014-10-1