DCMIP-2025: Introducing an Idealized Squall Line Test Case for Nonhydrostatic Dynamical Cores

We introduce a new suite of idealized test cases for the dynamical cores of atmospheric General Circulation Models. The tests were developed for the 2025 Dynamical Core Model Intercomparison Project (DCMIP-2025) which took place at the National Center for Atmospheric Research (NCAR) in June 2025 alongside a summer school (https://dcmip.org). The test suite was designed to probe (a) the impact of topography on atmospheric flows at various scales (see also the EGU 2026 companion paper led by Timothy Andrews); (b) a convection (squall line) test case; and (c) idealized experiments for atmospheric machine learning emulators.

This presentation focuses on the squall line test case, which challenges nonhydrostatic dynamical cores to accurately simulate moist convection and squall line dynamics at kilometer-scale resolutions. The scenario incorporates simplified moisture feedbacks using a warm-rain Kessler parameterization and is implemented across a range of horizontal (0.25–4.0 km) and vertical (250–500 m) grid spacings on a reduced-radius sphere. We assess three leading nonhydrostatic dynamical cores: the nonhydrostatic version of the Department of Energy/NCAR ‘Spectral Element’ model (called HOMME or SE), the ‘Model for Prediction Across Scales’ (MPAS), and NOAA’s Finite-Volume cubed-sphere dynamical core FV3. These are all available within NCAR’s Community Atmosphere Model (CAM) which is the atmospheric component of the Community Earth System Model (CESM).

Our analysis examines the numerical convergence characteristics, model-to-model variability, and the influence of core-specific dissipation mechanisms on the simulated convective storms. The results demonstrate the test case’s potential as a rigorous benchmark for future core development and model intercomparison efforts. This work contributes to advancing robust evaluation frameworks for atmospheric models in the kilometer-scale, nonhydrostatic regime.