Authors:

Georg S. Voelker, Gergely Bölöni, Young-Ha Kim, Günther Zängl, and Ulrich Achatz

Read the full paper here

Abstract:

Parameterizations for internal gravity waves in atmospheric models are traditionally subject to a number of simplifications. Most notably, they rely on both neglecting wave propagation and advection in the horizontal direction (single-column assumption) and an instantaneous balance in the vertical direction (steady-state assumption). While these simplifications are well justified to cover some essential dynamic effects and keep the computational effort small, it has been shown that both mechanisms are potentially significant. In particular, the recently introduced Multiscale Gravity Wave Model (MS-GWaM) successfully applied ray-tracing methods in a novel type of transient but columnar internal gravity wave parameterization (MS-GWaM-1D). We extend this concept to a three-dimensional version of the parameterization (MS-GWaM-3D) to simulate subgrid-scale nonorographic internal gravity waves.

The resulting global wave model—implemented into the weather forecast and climate code Icosahedral Nonhydrostatic (ICON)—contains three-dimensional transient propagation with accurate flux calculations, a latitude-dependent background source, and convectively generated waves. MS-GWaM-3D helps reproduce expected temperature and wind patterns in the mesopause region in the climatological zonal mean state and thus proves a viable internal gravity wave (IGW) parameterization. Analyzing the global wave action budget, we find that horizontal wave propagation is as important as vertical wave propagation. The corresponding wave refraction includes previously missing but well-known effects such as wave refraction into the polar jet streams. On a global scale, three-dimensional wave refraction leads to a horizontal flow-dependent redistribution of waves such that the structures of the zonal mean wave drag and consequently the zonal mean winds are modified.

Plain Language Summary:

This study introduces MS-GWaM, a three-dimensional model designed to simulate atmospheric gravity waves generated by mountains. Unlike traditional models that assume steady-state conditions, MS-GWaM accounts for transient, time-dependent effects, providing a more accurate representation of how these waves interact with the atmosphere. The model successfully captures phenomena such as wind reversals at high altitudes caused by wave breaking, which steady-state models often miss. This advancement enhances our understanding of atmospheric dynamics and improves the accuracy of weather and climate predictions.