Circumventing the pole problem of reduced lat‐lon grids with local schemes. Part II: validation experiments

Conditions for a horizontal discretization scheme to circumvent the pole problem of reduced latitude-longitude grids in spherical coordinates have been determined in Part I, and a forecast model built on these principles (GRASS) has been developed to solve the shallow-water equations on the sphere with various accuracy orders in space. Validation experiments are presented here with the main goal to assess the capacity of the model to perform stable, smooth and accurate forecasts with weak filter strengths, even at very high resolution. The selection of test-cases presented here includes a stationary solid-body rotation flow over the poles, and a stationary parallel flow with a curved profile of the velocity at poles. A demanding recently proposed test-case is finally examined in detail, for non-rotated and rotated coordinates. All test results indicate that the model is able to reach the initial objectives.