A new dynamical framework of nonhydrostatic global model using the icosahedral grid

For a nonhydrostatic global model that is run efficiently at super-high resolution, we propose the use of an icosahedral grid, which is one of the quasi-homogeneous grid systems. In this paper, we concentrate mainly on the description of the numerical scheme of a new dynamical framework using the icosahedral grid. The numerical method guarantees conservations of mass and total energy. To reduce the computational cost, the time-splitting scheme is employed and the set of equations is solved explicitly in the horizontal directions and implicitly in the vertical direction. This scheme only requires solving a one-dimensional Helmholtz equation for the vertical momentum. With the combination of this conservative nonhydrostatic scheme and the icosahedral grid, it is expected that the new model will efficiently run for super-high resolution simulations.

For the first assessment of the performance of the new dynamical core, we performed fundamental wave propagation tests; acoustic waves, gravity waves, mountain waves, equatorial waves, and planetary waves. In order to check the performance as a climate model, we also performed the Held-Suarez Test Case as a statistical test. As a result, our model result has good correspondence with that of other established models.