The Impact of Non-Orographic Gravity Waves on Transport and Mixing: Effects of Oblique Propagation and Coupling to Turbulence

Gravity waves (GWs) are a fundamental driver of circulation, tracer transport, and mixing in the middle and upper atmosphere, but their treatment in global circulation models remains incomplete. In particular, standard parameterizations typically restrict propagation to the vertical and treat GW–turbulence interactions in only a rudimentary manner, potentially leading to systematic biases in simulated dynamics and transport. This manuscript uses the Multi-Scale Gravity-Wave Model (MS-GWaM) implemented in Community Climate Icosahedral Nonhydrostatic Model UA-ICON, together with a novel theoretical framework to quantify the impact of (i) oblique GW propagation and (ii) explicit bidirectional coupling between GWs and turbulence. The Ensemble simulations for non-orographic GWs reveal that allowing for oblique propagation lowers and cools the summer mesopause by shifting the deposition of momentum and heat to lower altitudes, reduces GW-induced vertical shear in the middle and lower atmosphere, and enhances turbulent kinetic energy (TKE) in the upper mesosphere and lower thermosphere. In contrast, coupling GWs to turbulence produces a nearly opposite mesopause response, lifting and warming the mesopause, while maintaining a reduction in wave-induced shear and further enhancing turbulence. Tracer experiments additionally show that turbulent coupling significantly increases mixing in regions of enhanced TKE with implications for chemical redistribution. These results demonstrate that both oblique GW propagation and GW–turbulence interactions exert leading-order controls on mesosphere–lower thermosphere circulation, temperature structure, and tracer transport. Neglecting these processes in global models likely contributes to biases in the Brewer–Dobson circulation, energy balance, and constituent distributions, underscoring the need for next-generation GW parameterizations that capture these effects.