A baroclinic instability test case for atmospheric model dynamical cores

Abstract A deterministic initial‐value test case for dry dynamical cores of atmospheric general‐circulation models is presented that assesses the evolution of an idealized baroclinic wave in the northern hemisphere. The initial zonal state is quasi‐realistic and completely defined by analytic expressions which are a steady‐state solution of the adiabatic inviscid primitive equations with pressure‐based vertical coordinates. A two‐component test strategy first evaluates the ability of the discrete approximations to maintain the steady‐state solution. Then an overlaid perturbation is introduced which triggers the growth of a baroclinic disturbance over the course of several days. The test is applied to four very different dynamical cores at varying horizontal and vertical resolutions. In particular, the NASA/NCAR Finite Volume dynamics package, the National Center for Atmospheric Research spectral transform Eulerian and the semi‐Lagrangian dynamical cores of the Community Atmosphere Model CAM3 are evaluated. In addition, the icosahedral finite‐difference model GME of the German Weather Service is tested. These hydrostatic dynamical cores represent a broad range of numerical approaches and, at very high resolutions, provide independent reference solutions. The paper discusses the convergence‐with‐resolution characteristics of the schemes and evaluates the uncertainty of the high‐resolution reference solutions. Copyright © 2006 Royal Meteorological Society