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

TL;DR

This study investigates how oblique gravity wave propagation and their coupling with turbulence influence atmospheric circulation, temperature, and mixing, revealing significant impacts on mesosphere-lower thermosphere dynamics and emphasizing improvements needed in climate models.

Contribution

The paper introduces a novel framework and ensemble simulations to quantify the effects of oblique GW propagation and turbulence coupling, highlighting their importance in atmospheric modeling.

Findings

Oblique propagation lowers and cools the summer mesopause.

Turbulence coupling lifts and warms the mesopause.

Turbulent coupling enhances mixing in the upper atmosphere.

Abstract

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. Here, we use the Multi-Scale Gravity-Wave Model (MS-GWaM) implemented in the 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. Ensemble simulations 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 the middle and lower atmosphere, and enhances turbulent kinetic energy 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, particularly 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.