Development of a Ground-to-Thermosphere General Circulation Model Based on NEPTUNE: Idealized Test Cases

The Naval Research Lab (NRL) is currently developing a whole atmosphere model that will extend into the thermosphere up to ~600 km. This model is based on the Navy Environmental Prediction System Utilizing the NUMA Engine (NEPTUNE), which has a nonhydrostatic dynamical core based on the deep-atmosphere Euler equations. NEPTUNE uses spectral elements for spatial discretization and features a suite of explicit and implicit-explicit (IMEX) time integrators. Our initial efforts are focused on model stability with a model lid up to ~150 km, which requires an appropriate set of idealized test cases to stress test the model. Inspired by the dynamical core model intercomparison project (DCMIP), a hierarchy of four idealized tests appropriate for a high-altitude, deep-atmosphere model is considered: 1) 1D column of fluid perturbed by an acoustic wave, 2) balanced zonal flow in an isothermal atmosphere, 3) balanced zonal flow with a realistic vertical temperature profile, and 4) flow over orography on a reduced-radius sphere. Case 1 is useful for evaluating explicit and IMEX time-integrators and addressing the growth of acoustic and gravity waves at high-altitudes. Cases 2 and 3 provide a test-bed for lid-raising experiments and an appropriate background state for Case 4. Numerical results indicate the importance of including deep-atmosphere effects in test cases to keep NEPTUNE stable with a model top of 150 km for a target horizontal resolution of 100 km and 72 hour time-integration. This work was sponsored by the Chief of Naval Research.