Development of a numerical solution method for advection terms and its application to the atmospheric dynamic model, PHYSIC

A numerical solution method, HIFI, for advection terms was developed. The method is a hybrid of the newly developed FI method, the first- and second-order upwind schemes. The excursion of the solution caused by the FI method is suppressed by applying the first- and second-order upwind schemes only at the grid points where the excursion of the solution is predicted. This limited use of the high-numerical-diffusion schemes can suppress the numerical diffusion to a reasonably low level. The FI method was designed so as to maximize on accuracy without loosing any stability due to the linear analysis. The accuracy and stability of the FI method vary according to the Courant number and other parameters. HIFI was adopted based on the meteorological sub-model of the numerical atmospheric dispersion model, PHYSIC. Predictability of wind speed in the lower atmosphere could be improved. It is considered that the HIFI method can be applied not only to the meteorological sub-mode in PHYSIC but also to the diffusion calculation of atmospheric radioactive materials.