AS1.31 | Internal Gravity Waves
EDI
Internal Gravity Waves
Co-organized by NP7/OS4
Convener: Claudia Stephan | Co-conveners: Katherine GraysonECSECS, Chantal Staquet, Ulrich Achatz
Orals
| Tue, 16 Apr, 08:30–10:10 (CEST)
 
Room M2
Posters on site
| Attendance Tue, 16 Apr, 16:15–18:00 (CEST) | Display Tue, 16 Apr, 14:00–18:00
 
Hall X5
Orals |
Tue, 08:30
Tue, 16:15
Internal gravity waves (IGWs) still pose major questions in the study of both atmospheric and ocean sciences, and stellar physics. Important issues include IGW radiation from their various relevant sources, IGW reflection at boundaries, their propagation through and interaction with a larger-scale flow, wave-induced mean flow, wave-wave interactions in general, wave breaking and its implications for mixing, and the parameterization of these processes in models not explicitly resolving IGWs. The observational record, both on a global scale and with respect to local small-scale processes, is not yet sufficiently able to yield appropriate constraints. The session is intended to bring together experts from all fields of geophysical and astrophysical fluid dynamics working on related problems. Presentations on theoretical, modelling, experimental, and observational work with regard to all aspects of IGWs are most welcome, including those on major collaborative projects, which seek to accurately parameterize the role of IGWs in numerical models.

Orals: Tue, 16 Apr | Room M2

Chairpersons: Katherine Grayson, Ulrich Achatz
08:30–08:40
|
EGU24-110
|
AS1.31
|
solicited
|
On-site presentation
Clément Vic and Bruno Ferron

Internal tides are key players in ocean dynamics above mid-ocean ridges. The generation and propagation of internal tides over the Mid-Atlantic Ridge (MAR) have been studied through theoretical and numerical models, as well as through moored, that is, one-dimensional, observations. Yet, observations remain sparse and often restricted to the vertical direction. Here we report on the first two-dimensional in situ observation of an internal tide beam sampled by a shipboard acoustic Doppler current profiler through a vertical section over the MAR. The beam is generated by the interaction of the barotropic tidal current with a supercritical abyssal hill that sits in the rift valley of the MAR. A vertical mode decomposition is carried out to characterize the spatio-temporal variability of the beam. Although the modal content of the velocity field is dominated by modes 1 to 3, higher modes display localized and not persistent bursts of energy. The use of an analytical theory for linear internal waves allows us to rationalize the observed velocity field and interpret it as the superposition of modal waves generated on the hill and propagating in the same direction. The observed beam is qualitatively reconstructed as the superposition of waves of modes 2 to 6. The velocity field was sampled seven times across the same section and displayed qualitatively different patterns, unveiling the complexity of the dynamics above the MAR. A ray tracing of modal waves shows that the refraction by mesoscale currents could explain the observed variability of the tidal beam.

How to cite: Vic, C. and Ferron, B.: Observed structure of an internal tide beam over the Mid-Atlantic Ridge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-110, https://doi.org/10.5194/egusphere-egu24-110, 2024.

08:40–08:50
|
EGU24-8235
|
AS1.31
|
ECS
|
On-site presentation
Jesus Reis, Juan Gomiz-Pascual, Álvaro Peliz, Rui Caldeira, and Miguel Bruno

There is a considerable number of coastal regions where the interaction of barotropic tidal currents with the stratified water column over seamounts or sill topographies generates large amplitude internal waves. An example of this is the internal bores generated around the main sill of the Strait of Gibraltar. It is known that the vertical mixing induced by these phenomena induces a relevant biological response in both the generation place and remote areas. The present work analyses the generation of this kind of internal waves in the northern half of the submarine ridge between Madeira and the Desertas Islands (Portugal). Here, the interaction of a rather intense barotropic tidal current with the stratified water column and the abrupt ridge topography leads to the creation of hydraulic jumps that evolve into internal bores and solitons, which radiate outwards from the sill. These bores can be formed at both sides of the sill (eastern and western sides) in synchrony with the barotropic flow direction. The hydraulic jump that gives rise to the internal waves is generated after supercritical conditions are established over the sill (internal Froude number, Fr >1). While supercritical conditions prevail, the internal bore stands trapped on the downstream side of the sill. With the weakening of the barotropic current, the supercritical conditions are lost (Fr <1), and the internal bore and subsequent solitons are released from the sill. Internal bores formed on the western side of the sill have greater amplitudes than those formed on the eastern side, and it seems to be related to the different orientations of the barotropic current concerning the longitudinal axis of the sill depending on the flow being eastward or westward. A smaller hydraulic jump is also formed during the eastward phase of the barotropic tidal current. This study is the first to document the internal wave activity in the SE of Madeira Island. It combines data from satellite images, in-situ campaigns, and moored instruments to allow the observation of the hydraulic conditions before, during, and after the generation events. Estimates of the vertical mixing using Richardson number and energy fluxes calculations helped identify internal wave events.

How to cite: Reis, J., Gomiz-Pascual, J., Peliz, Á., Caldeira, R., and Bruno, M.: Observations of internal wave generation in Madeira island , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8235, https://doi.org/10.5194/egusphere-egu24-8235, 2024.

08:50–09:00
|
EGU24-13389
|
AS1.31
|
ECS
|
On-site presentation
Ashley Barnes

Internal waves propagate on the ocean stratification and carry energy and momentum through the ocean interior. The two most significant sources of these waves in the ocean are surface winds and oscillatory tidal flow across topography. We propose a hybrid of these two mechanisms, in which wind induced oscillations of sea surface and isopycnal heights are rapidly communicated to the seafloor via hydrostatic pressure. In the presence of topography, the resulting oscillatory bottom velocity may then generate internal waves in a similar manner to the barotropic tide. We investigate this mechanism in an idealised numerical isopycnal model of a storm passing over a mid ocean ridge, and perform several perturbation experiments in which ocean and wind properties are varied. Bottom-generated internal waves are identified propagating away from the ridge in the wake of the storm. Estimates of the total wave energy suggest that in the right circumstances these waves could be a significant source of internal wave energy, with a local wind work to wave energy conversion rate of up to 50% of the corresponding conversion to surface generated near-inertial waves in our domain. Our results suggest a need for further investigation in less idealised scenarios to more precisely quantity this novel mechanism of deep ocean wave generation, and how it may affect abyssal mixing. 

How to cite: Barnes, A.: Topographically-generated near-internal waves as a response to winds over the ocean surface, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13389, https://doi.org/10.5194/egusphere-egu24-13389, 2024.

09:00–09:10
|
EGU24-7578
|
AS1.31
|
ECS
|
On-site presentation
Friederike Pollmann, Jonas Nycander, Gaspard Geoffroy, Carsten Eden, and Dirk Olbers

The main forcing of the ocean’s internal gravity wave field is the interaction of the barotropic tide with the rough seafloor. This process is inherently anisotropic: the orientation of the topographic obstacles and the direction of the tidal currents determine the amount and direction of the generated internal wave of tidal frequency, the internal tide. Available global estimates of the internal tide generation, however, do not take this directionality into account. We present estimates of the global M2-tide generation into the first 10 vertical normal modes using a new method based on linear theory that resolves both magnitude and direction. Linear theory breaks down once the slope of the topographic obstacle exceeds that of the generated tidal beam. We discuss the role of such supercritical slopes at continental shelves and in the open ocean. Finally, we will use the anisotropic M2-tide generation as forcing of the internal wave model IDEMIX, the backbone of an energetically consistent parameterization of wave-induced turbulent mixing for ocean general circulation models. Both wave energy levels and turbulent kinetic energy dissipation differ substantially compared to the reference scenario with the previously used isotropic tidal forcing. This underlines the importance of resolving the directionality of the internal tide generation in parameterizations of wave-induced turbulent mixing.

How to cite: Pollmann, F., Nycander, J., Geoffroy, G., Eden, C., and Olbers, D.: Internal tide generation from linear theory: Supercritical slopes, directionality, and ocean mixing implications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7578, https://doi.org/10.5194/egusphere-egu24-7578, 2024.

09:10–09:20
|
EGU24-12622
|
AS1.31
|
ECS
|
On-site presentation
Yanmichel A. Morfa Avalos and Claudia C. Stephan

This study investigates the spectral energy budget of the atmosphere using storm-resolving simulations from two state-of-the-art global circulation models. We examine different hypotheses to explain the mesoscale κ-5/3 spectrum of horizontal kinetic energy (HKE). These hypotheses include the direct forcing due to inertia-gravity waves (IGWs), a downscale cascade mediated by weakly interacting IGWs, or interactions between waves and the mean flow. The resolved mesoscale energy fluxes within the upper troposphere and the lower stratosphere reveal different dynamics between the two layers. The lower stratosphere is mainly energized by direct forcing due to vertically propagating IGWs, with a negligible HKE cascade. The primary contribution to the mesoscale energy spectrum in the troposphere is from spectral transfers across scales, while the direct forcing due to IGWs is limited. However, the normal mode decomposition of the circulation into linear Rossby waves and IGWs suggests that their interactions dominate the downscale cascade at mesoscales. This result aligns with the hypotheses that explain the downscale cascade based on resonant triad interactions between vortical and gravity-wave modes. Furthermore, it is shown that wave-wave interactions do not contribute to the resolved energy transfers, challenging the hypothesis that the downscale cascade is due to weakly nonlinearly interacting IGWs.

How to cite: Morfa Avalos, Y. A. and Stephan, C. C.: The Role of Inertia-Gravity Waves in the Mesoscale Energy Transfers from Global Storm-Resolving Simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12622, https://doi.org/10.5194/egusphere-egu24-12622, 2024.

09:20–09:30
|
EGU24-18795
|
AS1.31
|
ECS
|
On-site presentation
|
Georg Sebastian Voelker, Young-Ha Kim, Gergely Bölöni, Günther Zängl, and Ulrich Achatz

Internal gravity waves are commonly parametrized in both weather and climate models to capture their important impacts on the large-scale resolved flow. To reduce the model complexity and increase the performance, these parametrizations typically neglect both the horizontal wave propagation, assuming a horizontally homogeneous local flow (columnar approximation), and the time dependence of the gravity wave dynamics (steady-state approximation). However, a number of studies have shown that these assumptions do not hold in general and might lead to systematic biases in the simulated atmosphere.

The recently introduced Multi-Scale Gravity Wave Model (MS-GWaM), implemented into the ICOsahedral Non-hydrostatic model (ICON), aims to relax the above-mentioned simplifications. In particular, the model simulates gravity waves with Lagrangian ray tracing methods while being coupled to the mean flow and allowing for a transient, three-dimensional propagation. In the current implementation, the model replaces the non-orographic wave drag parametrization.

We find that the 3-dimensional propagation and refraction of gravity waves and the correspondingly modified momentum/energy transport pathways have a significant impact on the middle atmosphere. For instance, the wave refraction around the Antarctic winter jet leads to the often observed convergence near the jet edges. Moreover, the horizontal propagation introduces wave drag at latitudes around 60°S and altitudes around 40 km – a region where it is typically missing in atmospheric models. The probability density functions of wave momentum fluxes exhibit the commonly observed long tails (i.e., wave intermittency) which cannot be reproduced with steady-state parameterizations. Additionally, the intermittent wave field's horizontal distribution displays significantly altered patterns. As an important consequence, the structure of the Quasi-biennial Oscillation (QBO) is significantly improved.

Recent efforts have focused on enhancing the model's efficiency, transforming it into a modular configuration, improving its general usability, and adapting it to work with the most recent version of ICON. By implementing these modifications, we aim to increase the accessibility of MS-GWaM to the community and thus establish a robust contribution to the ICON ecosystem.

How to cite: Voelker, G. S., Kim, Y.-H., Bölöni, G., Zängl, G., and Achatz, U.: The effect of transient lateral internal gravity wave propagation on the resolved atmosphere in ICON/MS-GWaM, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18795, https://doi.org/10.5194/egusphere-egu24-18795, 2024.

09:30–09:40
|
EGU24-3929
|
AS1.31
|
On-site presentation
Manfred Ern

The quasi-biennial oscillation (QBO) is the dominant mode of atmospheric variability in the tropical stratosphere. It has effects on the weather and climate in the tropics and the extratropics. The QBO is a wave-driven circulation pattern of alternating easterly and westerly winds that propagate downward with time. Climate models have problems in simulating a realistic QBO because of problems in simulating the QBO wave driving in a realistic way. Both mesoscale gravity waves and global-scale tropical waves contribute to the wave driving of the QBO, but the relative contribution of the different wave types is not well known.
For the period 2018 until mid 2023 we estimate the QBO driving by gravity waves from the residual in the TEM momentum budget for three modern reanalyses (ERA5, MERRA2, and JRA55) and compare absolute values of the QBO gravity wave driving with estimates derived from temperature observations of the SABER satellite instrument. Qualitatively, good agreement is found, but MERRA2 gravity wave driving seems to be too strong in the upper stratosphere. Further, we derive the QBO eastward driving by global-scale Kelvin waves for the reanalyses and from SABER observations. The QBO eastward driving by Kelvin waves is similarly strong as the gravity wave eastward driving, and again good agreement is found between SABER and the reanalyses. In the reanalyses below 30km the total westward driving of the QBO by global-scale waves, however, seems to be weaker than the estimated gravity wave driving.

How to cite: Ern, M.: Driving of the QBO by gravity waves and global-scale waves: a comparison between satellite data and reanalyses, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3929, https://doi.org/10.5194/egusphere-egu24-3929, 2024.

09:40–09:50
|
EGU24-2472
|
AS1.31
|
On-site presentation
Raj Rani, François Lott, Charles McLandress, Aurélien Podglagen, Andrew Bushell, Martina Bramberger, Hyun-Kyu Lee, M. Joan Alexander, James Anstey, Hye-Yeong Chun, Albert Hertzog, Bernard Legras, Elisa Manzini, Scott Osprey, Riwal Plougonven, John Scinocca, Javier Serrano, Federico Serva, Tim Stockdale, and Stefan Versick and the Strateole 2 and QBOi contributors

Gravity Waves (GWs) parameterizations from 14 General Circulation Models (GCMs) participating to the Quasi-Biennial Oscillation initiative (QBOi) are directly compared to Strateole-2 balloon observations made in the lower tropical stratosphere from November 2019 to February 2020 (phase 1) and from October 2021 and January 2022 (phase 2). The parameterizations span the 3 leading edge techniques used in GCMs to represent subgrid scale non-orographic GWs, the two globally spectral techniques developed by Hines (1997) and Warner and McIntyre (1999) respectively and the "multiwaves" approaches following Lindzen (1981). The input meteorological fields necessary to run the parameterizations offline are extracted from the ERA5 reanalysis and correspond to the instantaneous meteorological conditions found underneath the balloons.  In general, the amplitudes are in fair agreement between measurements of the momentum fluxes due to waves with periods less than 1 hr and the parameterizations. The correlation of the daily values between the observations and the results of the parameterization can be around 0.4, which is statistically significant elevated considering that we analyse around 1200 days of data and quite good considering that the parameterizations have not been tuned: the schemes used are just the standard ones that help producing a Quasi-Biennial Oscillation (QBO) in the corresponding model. These correlations nevertheless vary considerably between schemes and depend little on their formulation (globally spectral versus multiwaves for instance). We therefore attribute this agreement to dynamical filtering, which all schemes take good care of, whereas only a few relate gravity waves to their sources. Except for one parameterization, significant correlations are mostly found for eastward propagating waves, which may be due to the fact that during both Strateole 2 phases the QBO phase is easterly at the altitude of the balloon flights. On the other hand, statistical properties, like pdf of momentum fluxes seem better represented in spectral schemes with constant sources than in schemes ("spectral" or "multiwaves") that relate GWs to their convective sources.

How to cite: Rani, R., Lott, F., McLandress, C., Podglagen, A., Bushell, A., Bramberger, M., Lee, H.-K., Alexander, M. J., Anstey, J., Chun, H.-Y., Hertzog, A., Legras, B., Manzini, E., Osprey, S., Plougonven, R., Scinocca, J., Serrano, J., Serva, F., Stockdale, T., and Versick, S. and the Strateole 2 and QBOi contributors: Comparison between non orographic gravity wave drag parameterizations used in QBOi models and Strateole2 constant level balloons                 , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2472, https://doi.org/10.5194/egusphere-egu24-2472, 2024.

09:50–10:00
|
EGU24-1826
|
AS1.31
|
ECS
|
On-site presentation
Ziyi Li, Junhong Wei, Xinghua Bao, and Y. Qiang Sun

This talk will present our recent published study of Li et al. (2023, QJ). With the development of advanced data assimilation and computing techniques, many modern global reanalysis datasets aim to resolve the atmospheric mesoscale spectrum. However, large uncertainties remain with respect to the representation of mesoscale motions in these reanalysis datasets, for which a clear understanding is lacking. The aforementioned challenges have served as a strong motivation to reveal and quantify their mesoscale differences. This study presents the first comprehensive global intercomparison of the tropospheric and stratospheric mesoscale kinetic energy and its spectra over two selected periods of summer and winter events among six leading high-resolution atmospheric reanalysis products: European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis v5 (ERA5), China Meteorological Administration Reanalysis (CRA), Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA2), National Centers for Environmental Prediction's Climate Forecast System version 2 (CFSv2), Japanese 55-year Reanalysis (JRA-55), and ECMWF Reanalysis-Interim (ERA-I). A state-of-the-art global operational model is adopted as a supplementary reference. Although all reanalysis datasets can reproduce broad distribution characteristics that are grossly consistent with the 9 km model, there are substantial discrepancies among them in magnitudes. The ability to capture mesoscale signals is closely linked to their resolutions, but it is also impacted by other factors, including, but not limited to, the selected types of energy, seasons, altitudes, latitudes, model diffusions, parametrization schemes, moist condition, assimilation methods, and observation inputs. Moreover, all datasets illustrate conclusive behaviors for the prevalence of the rotational component in the troposphere, whereas only very few products fail to exhibit the dominance of the divergent component in the stratosphere. Overall, stratospheric ERA5 and CFSv2 outperform the other reanalysis datasets, and only these two can reproduce the feature of the canonical kinetic energy spectrum with a distinct shift from a steeper slope (approximately −3) at lower wave numbers to a shallower slope (approximately −5/3) at higher wave numbers. In addition, the relative disparities among datasets increase dramatically with height, and they are more pronounced in the divergent component. It is also found that the correlations among these datasets are much weaker in the Tropics.

Reference:

Li, Z., J. Wei, X. Bao, and Y. Q. Sun, 2023: Intercomparison of tropospheric and stratospheric mesoscale kinetic energy resolved by the high-resolution global reanalysis datasets. Quarterly Journal of the Royal Meteorological Society, 149(757), 3738–3764, https://doi.org/10.1002/qj.4605.

How to cite: Li, Z., Wei, J., Bao, X., and Sun, Y. Q.: Intercomparison of Tropospheric and Stratospheric Mesoscale Kinetic Energy Resolved by the High-Resolution Global Reanalysis Datasets, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1826, https://doi.org/10.5194/egusphere-egu24-1826, 2024.

10:00–10:10
|
EGU24-21740
|
AS1.31
|
On-site presentation
Neil Hindley, M. Joan Alexander, Martina Bramberger, Manfred Ern, Lars Hoffmann, Laura Holt, Riwal Plougonven, Inna Polichtchouk, Claudia Stephan, Annelize van Niekerk, and Corwin Wright

Modern numerical modelling simulations of the Earth's atmosphere have developed over the recent decades to ever finer spatial resolutions, allowing for a greater portion the atmospheric gravity wave (GW) spectrum to be resolved. Specialised global simulations with kilometre-scale resolutions have been performed offline that can resolve very large portions of the GW spectrum in the lower stratosphere and, as such, the balance between resolved and parameterised (unresolved) GW forcing in today's numerical simulations of the middle atmosphere is shifting. However, these kilometre-scale simulations are still too computationally costly to perform routinely and can quickly deviate from their initial conditions, which makes validating the resolved gravity waves in these simulations with satellite observations challenging. For this reason, a growing number of studies are using resolved GWs in lower-resolution stratospheric reanalyses as proxies for GWs in the real atmosphere, due to the apparent reliability, long timescale, global coverage and real-date data assimilation of these reanalysis products. However, these resolved GWs in reanalyses have not been widely tested or compared to satellite observations of GWs to assess their realism. One reason why such a comparison has been so challenging is due to the different ranges of GW wavelengths to which any given model or observational instrument is sensitive due to its grid spacing or sampling and resolution limits, an effect known as the observational filter. Therefore, any like-for-like assessment of resolved GWs in reanalysis using satellite observations must be able to sample the model using the exact sampling and resolution of the instrument. Here we use 3-D satellite observations from AIRS/Aqua to evaluate the realism of resolved stratospheric gravity waves in ERA5 reanalysis produced by the European Centre for Medium Range Weather Forecasts (ECMWF). We carefully apply the sampling and resolution limits of AIRS to the model using a full 3-D weighting function for each measurement footprint to create synthetic measurements of the ERA5 stratosphere as if were viewed by AIRS. We then follow identical processing steps to detrend, regrid and spectrally analyse both the real and synthetic measurements to recover localised GW amplitudes, wavelengths and directional momentum fluxes between 25 and 45 km altitude. We investigate the global momentum budget of GWs in reanalysis compared to observations and compare the seasonality and spectral properties of GWs over known stratospheric hot spots. Our preliminary results suggest that AIRS measurements exhibit more frequent large-amplitude wave events at larger horizontal wavelengths (greater than 150km) and larger net momentum fluxes overall than equivalent ERA5 measurements. Our satellite-sampling approach is applicable to any GW-resolving model, and sets out a potential roadmap towards more direct validation and comparison of resolved mesoscale dynamics in numerical models that could help to guide developments in the coming era of high-spatial resolution atmospheric modelling.

How to cite: Hindley, N., Alexander, M. J., Bramberger, M., Ern, M., Hoffmann, L., Holt, L., Plougonven, R., Polichtchouk, I., Stephan, C., van Niekerk, A., and Wright, C.: How realistic are resolved gravity waves in ERA5 reanalysis compared to satellite observations?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21740, https://doi.org/10.5194/egusphere-egu24-21740, 2024.

Posters on site: Tue, 16 Apr, 16:15–18:00 | Hall X5

Display time: Tue, 16 Apr 14:00–Tue, 16 Apr 18:00
Chairpersons: Ulrich Achatz, Katherine Grayson
X5.32
|
EGU24-17446
|
AS1.31
|
ECS
Sothea Has

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.

X5.33
|
EGU24-2227
|
AS1.31
|
ECS
Kun Liu, Xu Chen, Peng Zhan, and Hui Wang

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.

X5.34
|
EGU24-7411
|
AS1.31
|
ECS
|
Irmgard Knop, Stamen Dolaptchiev, and Ulrich Achatz

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.

X5.35
|
EGU24-9667
|
AS1.31
|
ECS
Felix Jochum, Ulrich Achatz, Ray Chew, and François Lott
Many operational gravity wave parameterizations rely on the single column and steady state approximations, thus neglecting horizontal propagation and transience. Recent studies indicate that these assumptions can lead to faulty predictions, motivating the development of more complex models. MS-GWaM, a Lagrangian gravity wave parameterization that has been in development for about a decade, is one such model that is based on a multi-scale WKB theory allowing for both transience and horizontal propagation. So far, it has been validated mainly for non-orographic gravity waves, however, a simple orographic source has already been implemented in a test version of the model, which is coupled to a pseudo-incompressible flow solver (PincFlow). The present study investigates that source in an idealized setting. For this purpose, the model is adjusted to PincFlow's recently implemented terrain-following coordinate system. In addition, the orographic source is supplemented with a blocked flow drag and a wave amplitude reduction that accounts for blocked layer formation. These are derived from background flow tendencies and gravity wave momentum fluxes in highly idealized, wave-resolving simulations. The model is then tested against the latter, using both the transient configuration and a newly implemented steady state mode. The comparison shows that allowing for transience results in a more accurate forcing of the resolved mean flow, especially when the orographic source is changing in time.

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.

X5.36
|
EGU24-11094
|
AS1.31
|
ECS
Alena Kosareva, Stamen Dolaptchiev, Ulrich Achatz, and Peter Spichtinger

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.

X5.37
|
EGU24-17716
|
AS1.31
|
ECS
|
|
Emily Lear, Corwin Wright, and Neil Hindley

Gravity wave sources such as convection are known to have a diurnal cycle, so it is expected that gravity waves should also follow a diurnal cycle. However, although this cycle can be simulated in models and observed in ground based data at fixed locations, it is difficult to observe in global satellite observations, due to their low time resolution, particularly since most gravity wave resolving instruments have sun-synchronous orbits and therefore always observe the same local solar time. In this study, GNSS radio occultation (GNSS-RO) data are used to investigate whether a diurnal cycle in gravity wave amplitudes can be seen in the stratosphere using these observations. Radio occultation uses GNSS signals received by a satellite that measures the bending angles and phase delay, due to these signals passing through the atmosphere. These measurements are randomly distributed in local solar time and have the high vertical resolution required to accurately resolve gravity waves. Specifically, in this work, GNSS-RO dry temperature data are used from multiple satellite missions, including COSMIC 1 and 2, Metop-A, -B and -C, and CHAMP. Wave amplitudes are found using the 1D S-Transform and the amplitudes are then binned in local solar time and averaged for each month, using all available data from the years 2001-2023. Consistent with theoretical observations, a diurnal cycle in gravity wave activity can be seen in the results and comparisons to convection data sets suggest this is strongly linked to convection. These results are also compared to wind data, which will affect the generation and filtering of the waves.

How to cite: Lear, E., Wright, C., and Hindley, N.: The diurnal cycle of gravity waves in GNSS-RO data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17716, https://doi.org/10.5194/egusphere-egu24-17716, 2024.

X5.38
|
EGU24-687
|
AS1.31
|
ECS
|
Cécile Le Dizes, Matthieu Mercier, Nicolas Grisouard, and Olivier Thual

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.

X5.39
|
EGU24-1666
|
AS1.31
|
ECS
Saranraj Gururaj and Anirban Guha

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.

X5.40
|
EGU24-1700
|
AS1.31
|
ECS
|
|
Arian Dialectaquiz, Marcelo Dottori, and Piero Mazzini

Through wavelet analysis of temperature and current data, and remote imaging via Synthetic Aperture Radar and True Color, internal waves were identified in the South Brazil Bight (SBB). These waves have predominant semi-diurnal tidal frequencies as well frequencies associated with cold fronts.

Through baroclinic energy flows and coarse graining kinetic energy budget calculated from results of the Regional Ocean Modeling System (ROMS), the energy cascade associated with this internal phenomenon was quantified, as well the contribution of topography in the generation of internal waves due to the instability of the internal tide.

The internal energy paths on the shelf were discretized with the correlation of sub - and supratidal energy flows with the Barotropic - Baroclinic conversion, thus identifying energy conversion hotspots by topography, and the spatial variability in the generation and propagation of internal waves.

The results indicate that while a supercritical regime of baroclinic tide generation prevails in the SBB, from the barotropic tide, with propagation towards the open sea, some regions on the continental shelf are close to a critical regime. In these areas, the lateral distance for the internal tide excursion is less than 5 km, which promotes shearing, local instability dissipation, and the generation of nonlinear internal waves. Simultaneously, in regions with a supercritical regime, subtidal frequency phenomena act as a force for internal waves towards the coast.

How to cite: Dialectaquiz, A., Dottori, M., and Mazzini, P.: Generation and paths of internal waves on a tropical continental shelf, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1700, https://doi.org/10.5194/egusphere-egu24-1700, 2024.

X5.41
|
EGU24-3251
|
AS1.31
|
ECS
Ray Chew, Stamen Dolaptchiev, Maja-Sophie Wedel, and Ulrich Achatz

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.

X5.42
|
EGU24-3904
|
AS1.31
Christoph Zülicke, Mozhgan Amiramjadi, and Sebastian Borchert

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.

X5.43
|
EGU24-5181
|
AS1.31
|
ECS
Iman Toghraei, François Lott, Laura Köhler, Claudia Stephan, and Joan Alexander

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.

X5.44
|
EGU24-8354
|
AS1.31
|
ECS
Petr Šácha and Dominika Hájková

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.

X5.45
|
EGU24-9725
|
AS1.31
|
Highlight
Markus Kunze, Tarique Siddiqui, Christoph Zülicke, Claudia Stolle, Claudia Stephan, Irina Strelnikova, Gerd Baumgarten, Robin Wing, Michael Gerding, and Sebastian Borchert

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.

X5.46
|
EGU24-10077
|
AS1.31
Nils Brüggemann, Martin Losch, Patrick Scholz, Friederike Pollmann, Sergey Danilov, Oliver Gutjahr, Johann Jungclaus, Nikolay Koldunov, Peter Korn, Dirk Olbers, and Carsten Eden

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.

X5.47
|
EGU24-18359
|
AS1.31
|
ECS
|
Highlight
Lukas Krasauskas, Jörg Gumbel, Linda Megner, Ole Martin Christensen, Nickolay Ivchenko, Björn Linder, and Donal Murtagh

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.

X5.48
|
EGU24-20640
|
AS1.31
|
ECS
|
Luke Rosamond, David Nolan, Yi Dai, and Chris Heale

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.

X5.49
|
EGU24-20995
|
AS1.31
Aman Gupta, Aditi Sheshadri, and M. Joan Alexander

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.