A baroclinic instability test case on an anelastic dynamical core

Because the hydrostatic assumption made in formulating the typical quasi-static system of equations tends to distort small-scale motions such as turbulence and convection, it is desirable in some applications to utilize a non-hydrostatic system of equations. The anelastic system - one designed to filter sound waves without invoking hydrostatic balance - was utilized at Colorado State University to develop a dynamical core based on a geodesic grid. To test this dynamical core, the baroclinic instability test case designed by Jablonowski and Williamson (2006) was modified for use in the anelastic sytem and performed here. During the perturbation version of the test, errors associated with grid seams developed and caused the expected baroclinic wave to distort and break prematurely. Similarly, an error with wavenumber 5 developed in the mid-latitudes during the steady state version of the test, suggesting this error is associated with the underlying model grid. Using an optimized grid reduced this error but did not eliminate it. These results indicate that further work is necessary to refine and improve the anelastic dynamical core used here.