Toward Transient Subgrid-Scale Gravity Wave Representation in Atmospheric Models. Part II: Wave Intermittency Simulated with Convective Sources

Abstract

In a companion paper, the Multi-Scale Gravity-Wave Model (MS-GWaM) has been introduced and its application to a global model as a transient subgrid-scale parameterization has been described. This paper focuses on the examination of intermittency of gravity waves (GWs) modeled by MS-GWaM. To introduce the variability and intermittency in wave sources, convective GW sources are formulated, using diabatic heating diagnosed by the convection parameterization, and they are coupled to MS-GWaM in addition to a flow-independent source in the extratropics accounting for GWs due neither to convection nor to orography. The probability density function (PDF) and Gini index for GWpseudomomentum fluxes are assessed to investigate the intermittency. Both are similar to those from observations in the lower stratosphere. The intermittency of GWs over tropical convection is quite high and found not to change much in the vertical. In the extratropics, where non-convective GWs dominate, the intermittency is lower than (comparable to) that in the tropics in the stratosphere (mesosphere), exhibiting a gradual increase with altitude. The PDFs in these latitudes seem to be close to the log-normal distributions. Effects of transient GW-mean-flow interactions on the simulated GWintermittency are assessed by performing additional simulations using the steady-state assumption in the GW parameterization. The intermittency of parameterized GWs over tropical convection is found to be overestimated by the assumption, whereas in the extratropics it is largely underrepresented. Explanation and discussion of these effects are included.

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

“…The model setup follows Kim et al. (2021). The Icosahedral Non‐Hydrostatic (ICON) model (Zängl et al., 2015) is used with its upper‐atmosphere extension (Borchert et al., 2019).…”

“…In the current setup, the single‐column approximation is used in MS‐GWaM, that is, lateral GW propagation is not taken into account. To represent the spectral characteristics and variability of tropical GWs, a subgrid convective source is used in MS‐GWaM (Kim et al., 2021).…”

“…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.…”

An application of WKBJ theory for triad interactions of internal gravity waves in varying background flows

“…Moreover, the WKBJ approach takes into account nonlinear interactions between GWs and a spatially and temporally varying mean flow. WKBJ theory is the basis of present‐day GW parametrizations, however for most applications relying on a steady‐state approximation where GWs instantaneously assume an equilibrium distribution defined by the available sources and the mean flow (Kim et al ., 2003;2020;Quinn et al ., 2020). While the GWs are modulated by the mean flow in this approximation, a GW impact on the mean flow is only possible once GWs dissipate, for example, by wave breaking.…”

Waves in the gas centrifuge: asymptotic theory and similarities with the atmosphere

“…It is these interactions that make gravity waves so important for atmospheric circulation. Despite their importance for weather and climate forecasting (Kim, Eckermann & Chun 2003;Orr et al 2010;Lott & Guez 2013;Kim et al 2021), considerable gaps in our understanding of the dynamics of gravity waves persist.…”