Contour Surgery Simulations of a Forced Polar Vortex

High-resolution simulations of a polar vortex disturbed by quasi-topographic forcing are performed using the method of “contour surgery”, a numerical method for inviscid flows wherein arbitrarily steep vorticity gradients can be formed and wherein scales of motion can vary over an extensive range. Simulations are performed of inviscid, incompressible, barotropic motion on the hemisphere, the sphere, and the plane. Comparisons with a hemispherical pseudospectral simulation show that accurate contour surgery simulations can be performed using a moderate number of contours to represent each hemisphere. Intermodel comparisons show that, although the overall evolution of the flow is qualitatively similar, there are noticeable differences. There is a significant difference between spherical and hemispherical calculations but, surprisingly, a remarkable agreement between spherical and planar calculations when a spatially varying planetary vorticity is used in the planar calculations.