Inclusion of Surface Topography into the Vector Vorticity Equation Model (VVM)

Surface topography is implemented into the vector vorticity equation model with a block representation of mountains in the height coordinate. The kinematic boundary conditions at the surface are satisfied with a proper computational boundary condition for vorticity. This approach has been tested in various ways, including idealized 2D mountain waves, the much-studied “Boulder Downslope Windstorm” case, and 3D orographic precipitation over a ridge with and without small-scale irregularities. The model performs reasonably well in all of these cases, with no obvious computational difficulties due to the use of coordinate surfaces intersecting the surface and is ready to be used for arbitrarily prescribed surface topography without any artificial smoothing.