New mountain-generated mesoscale flow test cases from DCMIP2025

The Dynamical Core Intercomparison Project (DCMIP) is an endeavour to evaluate and compare dynamical cores through the application of idealised test cases. Previous editions of DCMIP, in 2008, 2012, and 2016, introduced many widely used cases, including baroclinic wave, tracer transport, supercell, and tropical cyclone tests. We present a new test case developed for the most recent edition of DCMIP, held in June 2025 (DCMIP2025). This case uses an easily implementable initial condition, with the addition of mountain orography, to generate nonlinear mesoscale flow phenomena. Two different orographies are considered, which lead to dynamics of a gap flow and vortex shedding. The gap flow case exhibits accelerated flow and the creation of a pair of symmetric lee vortices, whilst the vortex shedding case instigates a flow reminiscent of a von Kármán vortex street. These tests are compared in four dynamical cores: three from the United States, along with GungHo, the compatible finite element dynamical core from the UK Met Office’s new LFRic model. Contrasting simulations with each dynamical core highlights differences in the numerical designs, including the grid choice and sources of numerical diffusion.