In this talk, we pursue the investigation of the relation between the large-scale flows and observed gravity wave momentum fluxes (GWMFs), starting from parameterizations and machine learning as two alternatives for predicting the gravity wave momentum fluxes in the lowermost tropical stratosphere. We investigate how much aggregation methods may allow to further improve on both alternatives, and what complementarity there may be between them. Observed gravity wave momentum fluxes are obtained from superpressure balloons during the Strateole 2 mission. The parameterizations come from the different climate models involved in the QBOi project, that have been compared to balloon measurements in Lott et al. (2023). The other predicted features are three tree-based ensemble machine learning algorithms, trained on part of the Strateole 2 dataset.  Three groups of aggregations are performed: aggregation among machine learning models, aggregation among parametrizations, and the aggregation between parametrizations and machine learning models. For the methodology, three aggregation methods are employed; two methods treat predictions from different models (parametrizations or machine learning) as features or information to be aggregated, while the remaining one uses both, inputs and predictions provided by those models.

The outcomes indicate that, despite struggling to estimate GWMFs individually, the collective information from various parametrizations proves valuable, particularly when combined with the large-scale flow variables. Additionally, the performance of the aggregation methods is sensitive to the choice of balloons. When the description of large-scale flows aligns well with the target GWMFs (balloon 2 and 8), all aggregation methods perform just as well as machine learning or the best-case scenario of parametrizations. Interestingly, there are also a few cases where machine learning and parametrizations perform poorly (correlation less than 0.2), yet their predictions, combined with large-scale information, can significantly elevate their performances more than 2 times (correlation larger than 0.5) in the aggregation methods (balloon 5). This suggests that existing parameterizations and machine learning approaches trained on observations have a complementarity that remains to be exploited. The present study was entirely offline, with no issue about the costs of computation. For practical applications, further investigation will be required to narrow down on the specific elements of parameterizations that are most informative.

How to cite: Has, S.: Aggregations of parametrizations and machine learning for gravity wave momentum flux reconstruction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17446, https://doi.org/10.5194/egusphere-egu24-17446, 2024.

The overreflection process of near-inertial internal waves (NIWs) has been theoretically predicted for several decades; however, to the best of our knowledge, this phenomenon has never been comprehensively investigated in real ocean scenarios. Based on the buoy observations collected several days after the passage of Typhoon Lekima in the Yellow Sea, a NIW surface overreflection event is clearly captured. The observed NIWs undergo nearly total reflection meridionally but are amplified zonally after reflection by approximately 20% in amplitude and 56% in vertically integrated horizontal kinetic energy. Ray tracing analysis indicates that the NIW was generated in the wake of Typhoon Lekima in the area north of the Shandong Peninsula and may propagated to the buoy station as coastal-trapped internal Kelvin waves. A simulation using a slab mixed layer model suggests that local wind work was insufficient to generate the amplified NIWs. The temporal evolution of near-inertial energy also implies that the intensified near-inertial waves cannot be attributed to the spontaneous generation resulting from unbalanced flows or the parametric subharmonic instability of M₂ internal tides during the reflection period. We found a high temporal correlation between the zonal NIW enhancement and the duration of a meridional lens-type shear flow after reflection, which is consistent with the Stern’s overreflection theory (Stern, 1977) that perpendicular background shear flow can feed energy to the incident NIWs. This indicates that the enhanced NIW may be stimulated by the near-surface reflection and the rotation effect plays a crucial role in the NIWs overreflection process in the real ocean. Furthermore, enhanced instability are found between the ocean surface and the upper thermocline after reflection. This study provides observational evidence that the background field could inject energy into the near-inertial band through NIW overreflection process, and may shed some light on understanding upper ocean mixing caused by NIW reflection.

How to cite: Liu, K., Chen, X., Zhan, P., and Wang, H.: Observations of near-inertial internal wave amplification and enhanced mixing after surface reflection, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2227, https://doi.org/10.5194/egusphere-egu24-2227, 2024.

The zonal-mean transport of tracers on a large scale, such as ozone and water vapor, is predominantly governed by the Brewer-Dobson circulation. However, this transport undergoes modifications influenced by small-scale gravity waves (GW) and turbulence resulting from GW breaking. As these dynamics are not completely resolved in weather and climate models, they necessitate parameterization. Given the significant impact of tracers on the Earth's energy budget and surface climate, understanding their transport variations is crucial for accurate atmospheric modeling. Presently, existing GW parameterization schemes neither account for the direct effects of GW tracer transport nor the enhanced tracer mixing due to GW breaking, but only for the indirect effect by driving the mean meridional circulation. Therefore, it becomes imperative to ascertain how and to what extent these small-scale phenomena modify the large-scale transport of tracers. To address this, we employ wave-resolving simulations, specifically investigating the impact of a three-dimensional wavepacket on tracer distribution using a pseudo-incompressible flow solver. Additionally, we extend a GW parameterization scheme, a Lagrangian ray tracer, to incorporate GW-induced tracer transport. Our research demonstrates the non-negligible direct impact of GW on tracer transport. Furthermore, we possibly discuss the influence of turbulent diffusive mixing on tracers. Our aim is to provide a comprehensive understanding of the intricate processes shaping large-scale tracer transport in the atmosphere.

How to cite: Knop, I., Dolaptchiev, S., and Achatz, U.: Impact of small-scale gravity waves on tracer transport, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7411, https://doi.org/10.5194/egusphere-egu24-7411, 2024.

How to cite: Jochum, F., Achatz, U., Chew, R., and Lott, F.: Validation of an orographic source in a Lagrangian gravity wave parameterization, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9667, https://doi.org/10.5194/egusphere-egu24-9667, 2024.

Cirrus clouds have a notable influence on radiation and, consequently, the energy balance. Therefore detailed understanding of ice physics processes is one of the keys to improving climate representation. Major drivers of the physical processes in ice clouds such as nucleation, freezing, sedimentation etc. are mostly triggered by local dynamical causes. The variability in vertical velocity, along with temperature and pressure fluctuations induced by gravity waves (GW), significantly impacts the formation and life cycle of cirrus clouds. However, conventional climate models and Numerical Weather Prediction (NWP) systems typically limit ice formation mechanisms to turbulent forcing.

This study is focused on the interaction between ice clouds and gravity waves, aiming to enhance the representation of these processes within coarse-grid model. Building upon a double-moment scheme for ice particles, a prototype parameterisation for the nucleation process induced by gravity waves was previously proposed in [1] and has been implemented in the ICON model for numerical verification and assessment. The current approach is targeting a comprehensive coupled description of ice physics and gravity wave interaction.

Information on subgrid-scale dynamical fields impacting cirrus formation is retrieved from Multi-Scale Gravity Wave Model (MS-GWaM) [2-5]. This gravity-wave parameterisation relies on WKB-theory and employs a raytracing-based technique. It allows for the consideration of transient wave dynamics and horizontal wave propagation. The chosen approach for joined description seeks to refine the physical representation of cirrus formation associated with both convectively generated gravity waves and gravity waves generated by sources other than orography and convection.

Preliminary results, incorporating an artificial periodic forcing term, demonstrate a good agreement of ice physics parameterisation with results from an explicitly integrated double-moment scheme, where processes such as nucleation are resolved in time. Ongoing efforts involve further coupling with the MS-GWaM parameterisation, with the goal of achieving a more physically accurate representation of ice formation zones. Additionally, an analysis of time-averaged characteristic quantities is planned for a comprehensive understanding of the system.

References

[1] S. I. Dolaptchiev, P. Spichtinger, M. Baumgartner, and U. Achatz. Interactions between gravity waves and cirrus clouds: Asymptotic modeling of wave-induced ice nucleation. Journal of the Atmospheric Sciences, 80(12):2861 – 2879, 2023.

[2] G. Bölöni, Y.-H. Kim, S. Borchert, and U. Achatz. Toward transient subgrid-scale gravity wave representation in atmospheric models. Part I: Propagation model including nondissipative wave–mean-flow interactions. Journal of the Atmospheric Sciences, 78(4):1317–1338, 2021.

[3] Y.-H. Kim, G. Bölöni, S. Borchert, H.-Y. Chun, and U. Achatz. Toward transient subgrid-scale gravity wave representation in atmospheric models. Part II: Wave intermittency simulated with convective sources. Journal of the Atmospheric Sciences, 78(4):1339–1357, 2021.

[4] U. Achatz, Y.-H. Kim, and G. S. Voelker. Multi-scale dynamics of the interaction between waves and mean flows: From nonlinear WKB theory to gravity-wave parameterizations in weather and climate models. Journal of Mathematical Physics, 64(11), 2023.

[5] Y.-H. Kim, G. S. Voelker, G. Bölöni, G. Zängl, and Ulrich Achatz. Crucial role of obliquely propagating gravity waves in the quasi-biennial oscillation dynamics. EGUsphere, 2023:1–18, 2023.

How to cite: Kosareva, A., Dolaptchiev, S., Achatz, U., and Spichtinger, P.: Interaction of cirrus clouds and gravity waves: towards a coupled representation in coarse resolution model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11094, https://doi.org/10.5194/egusphere-egu24-11094, 2024.

Internal tides, generated by the interaction of tidal flows with underwater topographies, play a pivotal role in ocean dynamics. They significantly contribute to energy transport in the oceans and can lead to deep-ocean mixing, influencing large-scale ocean circulation and ecosystems through nutrient transport. Their accurate representation in large-scale numerical models is essential to improve our understanding of oceanic processes and assess their impact on climate scenarios. However, implementing internal tide generation is challenging due to the variety of spatial and temporal scales involved. It cannot be tackled by estimations from observations and/or numerically expensive regional models alone. In this context, analytical methods offer insights to accurately describe the internal tide wavefield, enabling more precise parameterizations in global ocean models. Existing analytical approaches are based on specific (limiting) assumptions, often considering two-dimensional situations or weak amplitude topographies.

Here, we present a boundary element method to compute the internal tide radiated for a prescribed barotropic tidal flow over any arbitrary localized three-dimensional topography. This method, based on a Green's functions approach, assumes linear Boussinesq generation for harmonic tidal forcing (hence with a weak-amplitude excursion) and uses vertical mode decomposition to express the wave velocity field and the energy flux of the internal waves radiated in all directions. The properties of the internal tide generated by an axisymmetric Gaussian topography for constant stratification are discussed in detail. Results for the sub-critical regime (internal wave slopes larger than the topography) are consistent with the Weak Topography Approximation in the limit of small seamounts and when the influence of the Coriolis frequency is negligible. A specific discussion is made regarding the influence of the Coriolis frequency on the direction of emission for the internal tide radiated by axisymmetric seamounts. An important result is that the direction where the internal tide flux is maximum is controlled by the relative importance of the Coriolis frequency with respect to the tidal frequency, the orientation of the tidal flow, and the geometrical properties of the topography. Interestingly, for topographies elongated in one specific direction, the role of the Coriolis effect becomes negligible; the orientation of the tidal forcing and the one associated with the topography alone control the angular dependency of the energy flux radiated.

Our work is a first approach to realistic analytical modeling of internal tide generation. It emphasizes the importance of considering the 3D effects for this problem.

How to cite: Le Dizes, C., Mercier, M., Grisouard, N., and Thual, O.: 3D modelling of internal tide generation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-687, https://doi.org/10.5194/egusphere-egu24-687, 2024.

Wave--topography interaction is one of the primary mechanisms through which internal wave energy cascades to small length scales in the oceans. At small length scales, internal waves become unstable and break down, leading to turbulent diffusion and mixing. Precise diffusivity parametrisations are crucial for modeling ocean flows accurately. We study the interactions of a mode-1 internal wave with an isolated topography in the presence of a steady, stable surface current. For various amplitudes of the surface current, we investigate scattering caused by Gaussian shaped topographies by independently varying height and slope. In the presence of a surface current, a mode-1 wave that propagates in the direction of the current (denoted by M1W) has different properties compared to a mode-1 wave that propagates against the current (denoted by M1C), and we focus on both M1W and M1C. For all the heights considered, for both M1W and M1C, the current does not have a singular effect: it can reduce or increase scattering depending on the slope of the topography. Scattering due to large amplitude topographies (even with a small slope) can be quite different in the presence of a surface current. However, scattering caused by small amplitude topographies does not change significantly even in the presence of strong surface currents. Topographies with very high slopes (commonly known as supercritical topographies) scatter M1C more compared to M1W. Finally, we provide a brief analysis of the generation of superharmonic waves due to wave--topography interactions that occur in the presence of a surface current.

How to cite: Gururaj, S. and Guha, A.: Internal wave topography interactions in the presence of a steady surface current, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1666, https://doi.org/10.5194/egusphere-egu24-1666, 2024.

The representation of subgrid-scale orography is a challenge in the physical parameterisation of orographic gravity-wave sources in weather forecasting. A significant hurdle is encoding as much physical information with as simple a spectral representation as possible on unstructured geodesic grids with non-quadrilateral grid cells, such as the one used in the German Weather Service's Icosahedral Nonhydrostatic Model. Other issues include scale awareness, i.e., the orographic representation has to change according to the grid cell size. This work introduces a novel spectral analysis method approximating a scale-aware spectrum of subgrid-scale orography on unstructured geodesic grids. The dimension of the physical orographic data is reduced by more than two orders of magnitude in its spectral representation. Simultaneously, the power of the approximated spectrum is close to the physical value. The method is based on well-known least-squares spectral analyses. However, it is robust to the choice of the free parameters, and tuning the algorithm is generally unnecessary. Numerical experiments involving an idealised setup show that this novel spectral analysis performs significantly better than a straightforward least-squares spectral analysis in representing the physical energy of a spectrum. Studies involving real-world topographic data are conducted, and competitive error scores within 10% error relative to the maximum physical quantity of interest were achieved across different grid sizes and background wind speeds. The deterministic behaviour of the method is investigated along with its principal capabilities and potential biases, and it is shown that the error scores can be iteratively improved if an optimisation target is known.

How to cite: Chew, R., Dolaptchiev, S., Wedel, M.-S., and Achatz, U.: A constrained spectral approximation of subgrid-scale orography on unstructured grids, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3251, https://doi.org/10.5194/egusphere-egu24-3251, 2024.

Gravity waves are an important driver of the circulation in the mesosphere / lower thermosphere and connect it to the atmospheric layers below. This vertical coupling is realized in multiple steps – primary waves rise, break and initiate secondary waves, which further rise. We study this process for stationary mountain waves in idealized simulations with the upper-atmosphere extension of the ICON model. The setup is for constant wind and stratification up to 120 km, where a sponge layer begins. In a series of simulations with various winds and mountain sizes, we follow the evolution of mountain waves including their breaking. Particular focus is on the diagnosis of wave-mean flow interaction and the associated generation of secondary gravity waves. In the vertical wavenumber spectra we find three peaks of them, all associated with lower frequency and longer horizontal wavelengths than the primary mountain wave. The parameters of primary and secondary waves are closely correlated, which adds to the understanding of multi-step vertical coupling.

How to cite: Zülicke, C., Amiramjadi, M., and Borchert, S.: Generation of secondary gravity waves in idealized UA-ICON simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3904, https://doi.org/10.5194/egusphere-egu24-3904, 2024.

We compare the parameterization schemes that represent gravity waves in the Atmospheric Component of the IPSL Climate Model (LMDZ6A) and the high-resolution ICOsahedral Nonhydrostatic Weather and Climate Model (ICON). Our focus lies in assessing the capabilities of the gravity wave drag schemes to predict zonal momentum fluxes derived from ICON. The parameterization is run offline using ICON meteorological fields coarse grained to a healpix grid with size representative of an ESM grid (around 100km x 100km). We then examine the temporal mean, horizontal mean, and zonal mean gravity wave stresses predicted by the parameterizations and compare them to the zonal momentum fluxes associated with the ICON subgrid scale fields (e.g. the motions that are filtered out during the coarse-graining). The investigation reveals that in the stratosphere, the parameterizations have some skill at predicting zonal momentum fluxes of ICON, and this without prior tuning. More specifically, the parameterized gravity wave stresses due to mountains, convection and fronts align reasonably well with the zonal momentum fluxes from ICON in the stratosphere, each scheme consistently playing a dominant role where it should (frontal waves dominating in the midlatitude storm tracks, convective waves in the tropics, and mountain waves over orography). This permits physical interpretations of the origin of the gravity waves predicted by ICON, but raises challenges when extending this comparison to the troposphere. There, the agreement between the parameterized stress and the ICON subgrid scale stress is much weaker, which is likely attributable to the fact that in the troposphere subgrid scale forced motions like convective cells produce stresses much larger than the gravity wave stresses.

How to cite: Toghraei, I., Lott, F., Köhler, L., Stephan, C., and Alexander, J.: Comparison between the gravity wave stress parameterized in a climate model and simulated by the high-resolution non-hydrostatic global model ICON, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5181, https://doi.org/10.5194/egusphere-egu24-5181, 2024.

Orographic gravity waves (OGWs) are an important mechanism for coupling of the free atmosphere with the surface, mediating the momentum and energy transport and influencing the dynamics and circulation especially in the stratosphere and above. Current global climate models are not able to resolve a large part of the OGW spectrum and hence, OGW effects have to be parameterized in the models. Typically, the only parameterized effect is the OGW induced drag. Despite producing the same quantity as an output and relying on similar assumptions (e.g. instantaneous vertical propagation), the individual OGW parameterization schemes differ in many aspects such as handling of the orography, the inclusion of non-linear effects near the surface and the tuning of the emergent free parameters.

This presentation introduces a recently published study by the authors, reviewing 7 different parameterizations used in 9 different CMIP6 models and reporting on pronounced intermodel differences in the vertical distribution and magnitude of the parameterized OGW drag that are partly tuning-dependent. Finally, we demonstrate how the OGW drag differences project to the intermodel differences in the stratospheric dynamics, documenting the crucial importance of the lower- stratospheric OGW drag that controls the resolved wave propagation from the troposphere to the stratosphere in both winter hemispheres.

How to cite: Šácha, P. and Hájková, D.: Parameterized orographic gravity wave drag controls extratropical stratospheric dynamics in CMIP6 models., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8354, https://doi.org/10.5194/egusphere-egu24-8354, 2024.

We carry out high-resolution nested simulations over Andøya (ALOMAR) with UA-ICON to compare and interpret observational data in the mesosphere collected during the NASA VortEx sounding rocket campaign in March 2023.

We apply UA-ICON with 250 levels and a model top at 150 km at a global horizontal resolution of R2B7 (~20 km) with subsequent one-way nesting with nests at R2B8 (~10 km), R2B9 (~5 km), R2B10 (~2.5 km) and R2B11 (~1.25 km) horizontal resolution. For the global domain, the dynamic situation during the campaign is specified (specified dynamics, SD) by nudging to ECMWF operational analyses up to an altitude of 50 km. At the 1.25 km resolution, UA-ICON resolves a substantial fraction of the GW spectrum. Therefore, GW parameterizations are turned off at this resolution to isolate the effects of resolved GWs.

The Rayleigh-Mie-Raman (RMR) lidars, operated by IAP in Kühlungsborn, Germany, and at ALOMAR on Andøya, Norway, support the VortEx campaign through observations of temperatures and winds up to about 80 km by providing detailed information about GW activity including vertical wavelengths.

We present first comparison results between the high-resolution nested UA-ICON simulation and the RMR observations for the VortEx campaign in March 2023.

The emphasis is on estimating the vertical energy spectra of resolved gravity waves for the different grid refinements, compared to vertical energy spectra from the lidar observations.

How to cite: Kunze, M., Siddiqui, T., Zülicke, C., Stolle, C., Stephan, C., Strelnikova, I., Baumgarten, G., Wing, R., Gerding, M., and Borchert, S.: High-resolution nested UA-ICON simulation compared to mesospheric observations of the NASA VortEx campaign at ALOMAR, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9725, https://doi.org/10.5194/egusphere-egu24-9725, 2024.

We evaluate the parameterization IDEMIX for vertical mixing by breaking internal gravity waves in three different non-eddy resolving ocean models, namely ICON-O, FESOM and MITgcm. 
To assess the impact of the new closure, we prescribe three different products for wave forcing by tidal flow over topography that encompass the current uncertainty of this process. 
We compare these sensitivity simulations with a reference simulation without IDEMIX of each model and analyze the model-independent effects on the ocean circulation and mixing.
In particular, we observe a stronger mixing work once IDEMIX is used which better agrees with observations.
Coherent model responses to the stronger mixing work from IDEMIX are a deepening of thermocline depth, a warming of the upper-ocean thermocline water masses and an increased strength of the upper Atlantic overturning cell.

How to cite: Brüggemann, N., Losch, M., Scholz, P., Pollmann, F., Danilov, S., Gutjahr, O., Jungclaus, J., Koldunov, N., Korn, P., Olbers, D., and Eden, C.: Parameterized internal wave mixing in three ocean general circulation models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10077, https://doi.org/10.5194/egusphere-egu24-10077, 2024.

MATS (Mesospheric airglow/Aerosol Tomography and Spectroscopy) is as Swedish satellite launched in November 2022. It observes O₂ A-band airglow in near-infrared and UV light scattered from noctilucent clouds (NLCs) in limb imaging geometry and provides global 3-D temperature and NLC data products. These data sets can be used to characterise individual gravity waves (GWs) by determining their amplitudes, wavelengths and propagation directions (i.e. determining the 3-D wave vector for each wave). This enables determination of GW momentum fluxes in the MLT region, as well as detailed studies on GW spectra, propagation and interactions with the mean flow. MATS data, in combination with some GW modelling, can also be used to study GW sources and dissipation.

This presentation will provide an overview of the MATS mission and the 3-D data products with the focus on GW observations. We will include examples of data along with some initial GW analysis, instrument sensitivity estimates and data quality evaluation.

How to cite: Krasauskas, L., Gumbel, J., Megner, L., Christensen, O. M., Ivchenko, N., Linder, B., and Murtagh, D.: MATS satellite mission - observing gravity waves in the MLT region with tomographic limb imaging, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18359, https://doi.org/10.5194/egusphere-egu24-18359, 2024.

Alongside topographic forcing, deep moist convection makes a significant contribution to the global budget of upward momentum transport by gravity waves. Long-lived thunderstorms with rotating updrafts, known as supercells, produce strong and highly variable vertical motions over several hours. This study uses an idealized modeling framework in WRF to simulate supercells and their associated gravity waves up to 60 km altitude for multiple different wind profiles and convective modes. In contrast to many previous studies, the supercell is brought to an end and the simulations continue until most of the wave energy has dissipated. Thus, upward momentum transport can be computed over the entire life cycle of the storm and its associated waves, providing a more complete picture of the total impact of the event. The shapes of the wind profiles in the upper troposphere and lower stratosphere are found to strongly control the total momentum and energy transported into the upper stratosphere, so varying the stratospheric wind profile illuminates the behavior of the gravity waves in the stratosphere, particularly their vertical propagation. We also investigate the extent to which different modes of supercell structure, such as high-precipitation, low-precipitation, and classic supercells, lead to different intensities and spectra of the resulting gravity waves. In addition, the WRF model diabatic heating and vertical motions will be used as forcing conditions for stratospheric models such as MAGIC and CGCAM for the purposes of 1) comparison to WRF results between 20 and 60 km, and 2) so that wave propagation, momentum transport, wave breaking, and momentum deposition can be evaluated to altitudes above 80 km.

How to cite: Rosamond, L., Nolan, D., Dai, Y., and Heale, C.: The Stratospheric Gravity Wave Field and Momentum Fluxes Produced by Isolated Supercells, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20640, https://doi.org/10.5194/egusphere-egu24-20640, 2024.

Internal gravity waves (GWs) exhibit both vertical and horizontal (lateral) propagation in the atmosphere, influenced by the background shear of the flow that supports them. GW model parameterizations, however, represent them in climate models assuming strict vertical propagation. This modeling assumption can have implications for modeled large-scale stratospheric circulation and variability. We use ERA5 reanalysis to produce the climatological distribution of resolved GW momentum fluxes and forcing in the stratosphere, and their composite evolution around prominent modes of extratropical stratospheric variability like sudden stratospheric warmings (SSWs) and springtime final warmings (FWs). The climatology reveals that lateral propagation leads to the formation of a belt of rich GW activity in the upper winter stratosphere, which is otherwise localized over orographic hotspots in the lower stratosphere. The resolved forcing due to lateral GW propagation is found to be roughly the same order of magnitude as resolved forcing due to vertical fluxes, underlining the importance of lateral propagation for future GW parameterizations. Strikingly different GW forcing profiles before vs. after SSWs and FWs, highlighting the strong two-way connection between GWs and the stratospheric mean flow.

How to cite: Gupta, A., Sheshadri, A., and Alexander, M. J.: Gravity Wave Lateral Propagation Prominence in the Extratropical Stratosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20995, https://doi.org/10.5194/egusphere-egu24-20995, 2024.