A Hough Spectral Model for Three-Dimensional Studies of the Middle Atmosphere

Abstract

Abstract A three-dimensional framework is developed for studying the middle atmosphere in relation to upper-tropospheric structure. The numerical model is formulated from the primitive equations in isentropic coordinates, which directly characterize diabatic processes forcing the Brewer–Dobson circulation. It is anchored in observed tropospheric variability, so integrations provide middle atmospheric behavior that tracks observed variations in the upper troposphere. The numerical framework is versatile and computationally efficient. It achieves enhanced performance by incorporating eigenfunctions of the primitive equations to represent structure spectrally in all three coordinates. Scale-selective dissipation can then be applied entirely at sixth order, which leaves all but the shortest vertical scales undamped. This feature allows vertical diffusion to be made small enough to represent stratospheric transport as advective (rather than diffusive) for most of the scales carried in the integration. Transpor...