High-Latitude Filtering in a Global Grid-Point Model Using Model Normal Modes

The aim of high-latitude filtering in the vicinity of the poles is to avoid the excessively short time steps imposed on an explicit time-differencing scheme by linear stability due to fast moving inertia-gravity waves near the poles. The model normal mode expansion toward the problem of high-latitude filtering in a global shallow water model using the same philosophy as that used by Daley for the problem for large timesteps in P.E. models with explicit time integration schemes was applied.