Application of a smooth terrain-following coordinate with layer-by-layer smoothed terrain on the high resolution GRAPES model

The high resolution GRAPES model, such as the GRAPES-3km model, has a higher degree of recognition of the terrain. The slope of the terrain that can be recognized by each coordinate plane in the model is also larger. The calculation errors of the pressure gradient force and mass advection are more prominent. The smooth terrain-following coordinate can attenuate these terrain errors by attenuating the terrain effects on the coordinate plane in a number of ways. The smooth terrain-following coordinate with layer-by-layer smoothed terrain was selected, and ideal test and batch simulation test were carried out based on the GRAPES-3km model. The test results show that using the smooth terrain-following coordinate with layer-by-layer smoothed terrain, model simulations of gravity wave are closer to analytical values compared to simulations using other terrain-following coordinates; monthly average errors for temperature and wind field simulations using the smooth terrain-following coordinate show a certain degree of attenuation, and monthly average precipitation score is also improved. The smooth terrain-following coordinate with layer-by-layer smoothed terrain demonstrates better simulation application effects in the GRAPES-3km model.