A mountain-generated mesoscale test case from DCMIP-2025: Gap flow and vortex shedding variants

Abstract. DCMIP-2025, the fourth instance of the Dynamical Core Model Intercomparison Project (DCMIP), introduced new test cases for the evaluation of dynamical cores for atmospheric General Circulation Models. This paper overviews one of these test cases focused on mesoscale dynamics generated by mountain orography, using simple initial conditions and varying surface profiles to produce nonlinear flows. This work investigates two orographies: a mountain chain that instigates a gap flow, and an isolated mountain which generates vortex shedding. These tests are used to compare four state-of-the-art dynamical cores: CAM-SE (spectral element), CAM-FV3 (finite volume cubed-sphere), and CAM-MPAS (Model for Prediction Across Scales) from NCAR's Community Atmosphere Model (CAM), along with GungHo, the dynamical core from the UK Met Office's new LFRic model. Simulation comparisons highlight the impact of model features such as the mesh and sources of numerical diffusion. This test, with its two variants, adds to the existing suite of cases that enable the rigorous examination and comparison of dynamical cores.