The Interaction between Atmospheric Gravity Waves and Large-Scale Flows: An Efficient Description beyond the Nonacceleration Paradigm

Abstract

With the aim of contributing to the improvement of subgrid-scale gravity wave (GW) parameterizations in numerical weather prediction and climate models, the comparative relevance in GW drag of direct GW–mean flow interactions and turbulent wave breakdown are investigated. Of equal interest is how well Wentzel–Kramer–Brillouin (WKB) theory can capture direct wave–mean flow interactions that are excluded by applying the steady-state approximation. WKB is implemented in a very efficient Lagrangian ray-tracing approach that considers wave-action density in phase space, thereby avoiding numerical instabilities due to caustics. It is supplemented by a simple wave-breaking scheme based on a static-instability saturation criterion. Idealized test cases of horizontally homogeneous GW packets are considered where wave-resolving large-eddy simulations (LESs) provide the reference. In all of these cases, the WKB simulations including direct GW–mean flow interactions already reproduce the LES data to a good accuracy without a wave-breaking scheme. The latter scheme provides a next-order correction that is useful for fully capturing the total energy balance between wave and mean flow. Moreover, a steady-state WKB implementation as used in present GW parameterizations where turbulence provides by the noninteraction paradigm, the only possibility to affect the mean flow, is much less able to yield reliable results. The GW energy is damped too strongly and induces an oversimplified mean flow. This argues for WKB approaches to GW parameterization that take wave transience into account.

A Comparison of Small‐ and Medium‐Scale Gravity Wave Interactions in the Linear and Nonlinear Limits

“…The need for transience and a move away from the single column approach are crucial for improving these schemes. The results in this paper support the conclusions of Senf and Achatz (), Ribstein et al (), and Bölöni et al () who found that using ray tracing techniques with WKB theory to include time dependence and horizontal propagation led to much better agreement with large eddy simulations models on wave‐mean flow interactions. It is noted that typical operational parameterizations work statistically and consider a broad spectrum of waves.…”

Global analysis for periodic variations in gravity wave squared amplitudes and momentum fluxes in the middle atmosphere

“…Additional processes that may lead to GW dissipation are radiative and turbulent damping (e.g., Marks and Eckermann, 1995). Even without dissipation GWs may exchange momentum and energy with the background wind, by either horizontal refraction (Buehler and McIntyre, 2003;Preusse et al, 2009) or transient nonlinear interactions (Sutherland, 2006;Muraschko et al, 2015;Boeloeni et al, 2016).…”

An intercomparison of stratospheric gravity wave potential energy densities from METOP GPS radio occultation measurements and ECMWF model data

“…Being mainly excited in the troposphere by flow over terrain, by convection, or by spontaneous emission, GWs may propagate both vertically and horizontally over large distances to deposit their momentum and energy far away from their source upon instability or transience (e.g., Fritts and Alexander, 2003;Sato et al, 2009Sato et al, , 2012Preusse et al, 2009;Bölöni et al, 2016). Thus, GWs are an important mechanism that couples the middle and upper atmosphere to the troposphere (e.g., Lübken et al, 2010, and references therein).…”