Toward Transient Subgrid-Scale Gravity Wave Representation in Atmospheric Models. Part I: Propagation Model Including Nondissipative Wave–Mean-Flow Interactions

Abstract

Current gravity-wave (GW) parameterization (GWP) schemes are using the steady-state assumption, where an instantaneous balance between GWs and mean flow is postulated, thereby neglecting transient, non-dissipative direct interactions between the GW field and the resolved flow. These schemes rely exclusively on wave dissipation, by GW breaking or near critical layers, as a mechanism leading to forcing of the mean flow. In a transient GWP, without steady-state assumption, non-dissipative direct wave-mean-flow interactions are enabled as an additional mechanism. Idealized studies have shown that this is potentially important, so that the transient GWP Multi-Scale Gravity-Wave Model (MS-GWaM) has been implemented into a state-of-the-art weather and climate model. In this implementation, MS-GWaM leads to a zonal-mean circulation well in agreement with observations, and increases GW momentum-flux intermittency as compared to steady-state GWPs, bringing it into better agreement with super-pressure balloon observations. Transient effects taken into account by MS-GWaM are shown to make a difference even on monthly time-scales: in comparison with steady-state GWPs momentum fluxes in the lower stratosphere are increased and the amount of the missing drag at Southern Hemispheric high latitudes is decreased to a modest but non-negligible extent. An analysis of the contribution of different wavelengths to the GW signal in MS-GWaM suggests that small scale GWs play an important role down to horizontal and vertical wavelengths of 50km (or even smaller) and 200m respectively.

Interaction Between Stratospheric Kelvin Waves and Gravity Waves in the Easterly QBO Phase

“…Instead of the operational GW parameterization of this model, we use a prognostic parameterization, the Multi-Scale Gravity Wave Model (MS-GWaM), which predicts the time evolution of GW action density field in positionwavenumber phase space (Achatz et al, 2017;Bölöni et al, 2021;Muraschko et al, 2015). A detailed description of MS-GWaM and its application to ICON is provided in Bölöni et al (2021). In the current setup, the single-column approximation is used in MS-GWaM, that is, lateral GW propagation is not taken into account.…”

“…The horizontal grid spacing is 160 km, and the vertical spacing is 700 m in the stratosphere. Instead of the operational GW parameterization of this model, we use a prognostic parameterization, the Multi‐Scale Gravity Wave Model (MS‐GWaM), which predicts the time evolution of GW action density field in position–wavenumber phase space (Achatz et al., 2017; Bölöni et al., 2021; Muraschko et al., 2015). A detailed description of MS‐GWaM and its application to ICON is provided in Bölöni et al.…”

“…A detailed description of MS‐GWaM and its application to ICON is provided in Bölöni et al. (2021). In the current setup, the single‐column approximation is used in MS‐GWaM, that is, lateral GW propagation is not taken into account.…”

“…Young-Ha Kim Borchert et al (2019). MS-GWaM and its code for the use within ICON have been developed at Goethe-Universität Frankfurt am Main and described in the companion papers Bölöni et al (2021) and Kim et al (2021). Open access funding enabled and organized by Projekt DEAL.…”

“…MS‐GWaM and its code for the use within ICON have been developed at Goethe‐Universität Frankfurt am Main and described in the companion papers Bölöni et al. (2021) and Kim et al. (2021).…”