A Study of Nonhydrostatic Equation Sets for Low- and High-Altitude Atmospheric Modeling

As part of the U.S. Navy’s coupled thermosphere-ionosphere prediction system, we are evaluating three candidate dynamical cores (DyCores) extending from the ground to the middle thermosphere (~300 km) for the neutral atmosphere component. The three perspective DyCores use 1) hybrid virtual potential temperature (HVPT) (Eckermann et al., 2023), 2) specific internal energy (SIE), and 3) total energy (TE), respectively, and are discretized in the spectral element based Nonhydrostatic Unified Model for the Atmosphere (NUMA). All three of these DyCores are valid for variable composition, deep-atmospheres.

All three DyCores conserve mass to machine precision, while the TE DyCore also conserves total energy. For low altitude idealized test case on reduced sphere which is variations of mountain-wave simulations designed for the Dynamical Core Model Intercomparison Project (DCMIP). The gravity waves generated by 3D Schär mountain are compared with the linear analytic solution. At high altitude, above 100 km, the variation in composition is taken into consideration for all three equation sets. Further, the pressure gradient force (PGF) is expressed in logarithmic form for stable simulations at high altitude. For high altitude, static (resting) atmosphere tests are performed with and without topography, followed by a linear gravity wave test using the three equation sets. The numerical results for different DyCores are quantitatively compared to propose the best configuration for both low and high altitude atmospheric predictions.

This work was funded by the Office of Naval Research Marine Meteorology and Space Weather program.