AS1.19
PICO: Mon, 24 Apr | PICO spot 5
The parameterization scheme that represents gravity waves due to convection in LMDz-6A, the atmospheric components of the IPSL coupled climate model (IPSLCM6), is directly compared to Strateole-2 balloon observations made in the lower tropical stratosphere from November 2019 to February 2020. The input meteorological fields necessary to run the parameterization offline are extracted from the ERA5 reanalysis and correspond to the instantaneous meteorological conditions found underneath the balloons. In general, we find a fair agreement between measurements of the momentum fluxes due to waves with periods less than 1hr and the parameterization. The correlation of the daily values between the observations and the results of the parameterization is around 0.4, which is statistically elevated considering that we analyse around 600 days of data and surprisingly good considering that the parameterization has not been tuned: the scheme is just the standard one that helps producing a Quasi-Biennial Oscillation in the IPSLCM6 model. Online simulations also show that the measured values of momentum fluxes are well representative of the zonally and averaged values of momentum fluxes needed in LMDz-6A to simulate a QBO. The observations also show that longer waves with periods smaller than a day carry about twice as much flux as waves with periods smaller than an hour, which is a challenge since the low period waves that make the difference are potentially in the “grey zone” of most climate models
How to cite: Lott, F., Rani, R., Podglajen, A., Codron, F., Guez, L., Hertzog, A., and Plougonven, R.: Comparison between a non orographic gravity wave drag scheme and constant level balloons in the QBO region, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-2661, https://doi.org/10.5194/egusphere-egu23-2661, 2023.
Vertical ascent due to gravity waves (GW) represents one important formation mechanism for cirrus clouds, i.e., clouds consisting solely
of ice crystals. Further, GWs can substantially influence the microphysical cloud properties and cloud life cycle, which are crucial
for the radiative impact of the cirrus clouds. Here we investigate the interactions between high-, mid- or low-frequency GWs and cirrus
clouds in the tropopause region. Utilizing asymptotic analysis reduced equations are derived for the self-consistent description of the
cirrus dynamics forced by a monochromatic GW. This allows for the construction of prototype parameterization of the number nucleated ice
crystals. The GW-cirrus interactions are studied further in cloud resolving large eddy simulation and the results are used to evaluate
the asymptotic parameterization.
How to cite: Dolaptchiev, S., Spichtinger, P., Baumgartner, M., and Achatz, U.: Cirrus cloud formation by gravity waves, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-6108, https://doi.org/10.5194/egusphere-egu23-6108, 2023.
Horizontally short gravity waves are often observed near the tropopause. Here, airborne observations of mountain waves over southern Scandinavia are used to characterize these waves and to detect non-stationary modes. A series of two-dimensional numerical simulations is used to explain the generation of these transient wave modes that are trapped in the lowermost stratosphere and propagate horizontally downstream along the tropopause inversion layer. The numerical results reveal on which external parameters the properties of the short waves depend on. It turns out that the interaction of wave breaking aloft in the middle atmosphere and the tropospheric flow is the essential process explaining the generation of these non-stationary modes. Their characteristics is controlled by the sharpness of the tropopause inversion layer, the strength of the orographic forcing and, partially, by the spectra of the underlying orography exciting the vertically propagating mountain waves.
How to cite: Dörnbrack, A.: Transient Tropopause Waves, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-4081, https://doi.org/10.5194/egusphere-egu23-4081, 2023.
From March to December 2014, Loon LLC flew 107 super-pressure balloons in the lower stratosphere over the Southern Ocean. Their GPS sampling frequency of 1Hz allowed them to sample motion associated with atmospheric internal gravity waves generated by the Andes mountains, small islands, and non-orographic sources such as fronts. Analyzing the balloons’ data time series using wavelets, we present distributions of the gravity waves’ momentum fluxes, phase speeds, and wavelengths, both in the time-mean and as they vary from month to month. Many climate models parameterize gravity waves using a phase speed-momentum flux relationship, so we focus on the relationship between those quantities.
How to cite: Green, B. and Sheshadri, A.: Gravity Wave Phase Speeds, Wavelengths, and Momentum Fluxes Observed Above the Southern Ocean, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9679, https://doi.org/10.5194/egusphere-egu23-9679, 2023.
Trapped lee waves and turbulent rotor activity are a hazard for aviation, so forecasters must take into account the likelihood of lee wave activity when advising aviation personnel. The UK Met Office’s operational high resolution Numerical Weather Prediction model, UKV, resolves lee wave activity but there is currently no automated operational way to recognise such regions directly from the high resolution UKV data, short of a forecaster looking at the data themselves. If lee waves can be detected from the UKV data, we can use this output to gain a better understanding of lee waves and their impact over Britain and Ireland. For example, over which regions are lee waves likely to form? Which atmospheric conditions are the most conducive to lee wave propagation?
A machine learning (ML) model, a U-Net, was trained to identify and segment lee waves, and then retrained to derive characteristics about the waves (orientation, wavelength) from the model data. The wave amplitudes are also extracted using the wave mask from the segmentation model. These ML models were then applied to a 30 year dataset (1982 – 2012) of high resolution NWP output, driven by ERA-Interim data. From this, the location and characteristics of lee waves over Britain and Ireland from within this time period were extracted. In this presentation, we explore the climatology of lee waves in the data over this period, including the relationship between waves and the orography; frequency of waves; seasonal effects; the effects of weather patterns on waves; and diurnal effects.
How to cite: Coney, J., Ross, A., Denby, L., Wang, H., Vosper, S., van Niekerk, A., and Dunstan, T.: A climatology of trapped lee waves over Britain and Ireland, derived using machine learning, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7629, https://doi.org/10.5194/egusphere-egu23-7629, 2023.
The SouthTRAC measurement campaign was held in Argentina from September to November 2019 using the HALO research aircraft. One of the main goals of the campaign was gravity wave (GW) study in the region of Southern Andes: a global hotspot for GW activity. The measurements included air temperature data from the IR limb imaging spectrometer GLORIA jointly developed by FZJ and KIT, as well as ALIMA, an upward looking lidar developed by DLR, and in situ instruments. GLORIA's viewing direction can be panned between 45° and 135° with respect to the flight direction. Combining this capability with flight paths that encircle the observed atmospheric region, multiple measurements of the same air mass can be performed, allowing for 3D tomography of the atmosphere with a vertical resolution down to 250 m and horizontal resolution of around 25 km. GLORIA provides data below the flight altitude of the HALO aircraft (up to 15 km), while ALIMA observations cover the altitude range between 20 and about 60 km. GLORIA is the airborne demonstrator of the satellite based infrared limb imager CAIRT proposed as the Earth Explorer 11 candidate.
During a research flight on 20-21 September, a large amplitude mountain wave was observed over the Andes. GLORIA 3D data showed a complex temperature structure with several overlapping gravity wave families at altitudes of 9 to 14 km above the mountain ridges. The amplitudes and 3D wave vectors for each of those families were determined by performing a least-squares fit of harmonic disturbances to the GLORIA temperature data. These wave parameters were then used to initialise a ray-tracer (GROGRAT ray-tracing code was used) and follow the path of the waves as they propagated upwards and away from the mountain range. The results of this study could be summarised as follows:
- Many of the waves observed by GLORIA in the 9-14 km altitude range propagated into the regions observed by ALIMA in 25-40 km altitudes. There was very good agreement between ALIMA data and GLORIA data-initialised ray tracing results: GWs observed by GLORIA were shown to propagate into the same regions where waves were seen by ALIMA and their spectral characteristics also closely matched ALIMA observations.
- Oblique GW propagation was directly observed, including propagation of some GWs toward the upwind side of the Andes mountain range. Oblique propagation also resulted in significant meridional transport of zonal gravity wave momentum flux (GWMF).
- We observed strong horizontal GW refraction, with some wave vectors turning by more than 50°. This resulted in significant momentum exchange between waves and the background flow outside of wave generation and breaking regions.
- We also use the GLORIA data to study the time dependence (as a result of changing winds) of the mountain wave pattern over the Andes.
How to cite: Krasauskas, L., Kaifler, B., Rhode, S., Ungermann, J., Woiwode, W., and Preusse, P.: Oblique propagation and refraction of mountain waves over the Andes observed by GLORIA and ALIMA during the SouthTRAC campaign, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-14959, https://doi.org/10.5194/egusphere-egu23-14959, 2023.
Gravity waves (GWs) transport energy within the atmosphere both in vertical and horizontal direction. While the former is considered in climate models via parameterizations, the latter is often not modeled in most long time simulations. Especially orographic GWs can propagate horizontally more than 1000 km from their sources, however, and thereby de- or accelerate winds in completely different regions. To remedy this, we present a model that is capable of describing orographic GW sources and the associated GWs and their propagation in the atmosphere. From this, we can approximate general propagation pattern, which in the following can be used in climate models (here EMAC) to improve the orographic GW parameterization. The first simulations show strong redistribution of wave drag from land masses and thereby a closing of the gap of missing wave drag at 60°S.
How to cite: Rhode, S., Eichinger, R., Preusse, P., Garny, H., and Krasauskas, L.: Modelling horizontal propagation of orographic Gravity Waves in climate models, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11529, https://doi.org/10.5194/egusphere-egu23-11529, 2023.
Internal gravity waves (GWs) have an important influence on the atmospheric energy transport and momentum budget. Consideration of the GWs – related processes is necessary in modelling and conceptual models of the atmosphere. GWs cover a broad spectrum of wavelengths from few to thousands of kilometres. Hence, they cannot be fully resolved by the global climate models (GCMs) and have to be parameterized. Although recent efforts with satellite observations and high-resolution models have been improving tuning and constraints of the GWs parameterizations, there is still a large uncertainty concerning the effects of GWs in GCMs. This is unwanted due to large impact of GWs on the atmospheric dynamics.
In our research we focus on orographic GW (OGW) parameterizations used in CMIP6 simulations. We compare the OGW induced drag from 7 different OGW parameterizations used in 9 different models, establishing the simulation-unique tuning of free parameters for majority of them. The comparison shows large, unexpected differences between simulations, which can be partly traced to the tuning or type of the parameterization. We also analyze intermodel differences in zonal mean winds and Eliassen-Palm flux divergence to trace the effects of the differences in OGW drag. Particularly, our results demonstrate a strong correlation between resolved wave drag and OGW drag in the models. Overall, our study gives an additional motivation for further improvements of the OGW parameterization schemes, with the aim of lowering the uncertainty of the future climate projections.
How to cite: Hájková, D., Šácha, P., and Pišoft, P.: Link between orographic gravity wave parameterizations and resolved dynamics in CMIP6 models., EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-4866, https://doi.org/10.5194/egusphere-egu23-4866, 2023.
Internal gravity waves (GWs) are a ubiquitous component of atmospheric dynamics, propagating both horizontally and vertically through the atmosphere, interacting with other flow components and affecting regional to large-scale dynamics. Due to the wide spectrum of GWs, model dynamics in general circulation models (GCMs) can resolve only part of the spectrum, leaving the effects of the unresolved part to be inserted by parametrisations. The analysis of high-resolution atmospheric datasets with resolved GWs allows us to understand GW dynamics and their effects on the mean flow, even in the long-term time-scales. In addition to this, such analysis enables validation of the parametrised effects and potential improvements of the parametrisations. In the presented work, we analyse resolved GWs in the ECMWF‘s ERA5 reanalysis, evaluating their effects on the flow through the GW drag.
How to cite: Procházková, Z., Pišoft, P., and Šácha, P.: Quantification of gravity wave drag in ERA5 reanalysis, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-4928, https://doi.org/10.5194/egusphere-egu23-4928, 2023.
Gravity waves are small-scale atmospheric waves which transport energy and momentum. These waves impact the large scale circulation and increasing our understanding of them is therefore important to support improvements to weather and climate models. This presentation focusses on gravity waves in the stratosphere using data from a high resolution run of the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS) operated at a kilometre-scale spatial resolution, the Atmospheric Infrared Sounder (AIRS) on NASA’s Aqua satellite and the ECMWF ERA5 reanalysis. For this comparison, the IFS run and ERA5 are resampled using the AIRS observational filter. Data are examined during the first 2 weeks of November, as the high resolution model was initialised on the 1st of this month. Wave properties were found using the 2D+1 S-Transform, a spectral analysis technique, which has been previously applied to AIRS data. Asia and surrounding regions are investigated, because preliminary studies of AIRS data suggested strong gravity wave activity in this region during this time period. Gravity waves can also be seen in the high resolution model and ERA5 data at similar times and locations as those in the observations. Higher amplitude gravity waves can be seen in nighttime AIRS data compared to the resampled models. The horizontal wavelengths in the data sets are generally similar in areas of peak gravity wave activity for nighttime data. Weather models are advancing rapidly and kilometre scales, such as the experimental IFS run, could become operational in the next decade. At these grid scales, gravity waves must be resolved instead of parameterized so the models need to be tested to see if they do this correctly. This work provides information on how a cutting edge model resolves gravity waves compared to observations.
How to cite: Lear, E., Wright, C., Hindley, N., and Polichtchouk, I.: Comparing gravity waves sampled from a kilometre-scale IFS run to AIRS satellite observations, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3495, https://doi.org/10.5194/egusphere-egu23-3495, 2023.
The Brewer-Dobson circulation (BDC) is a meridional circulation mainly driven through mean-flow forcing by Rossby-wave breaking that is, however, also influenced by gravity waves (GW). As some part of GW dynamics is subgrid-scale in numerical climate and weather prediction models, an appropriate wave parameterization and later an accurate separation of the drivers are necessary to understand the impact of the subgrid-scale GWs on the BDC.
Polichtchouk et al. (2018) explored the sensitivity of BDC to the parameterized GW drag by separating the drivers of the residual circulation using the downward-control principle. Even in relatively high-resolution simulations, the parameterized drags are found to significantly contribute to the BDC in the lower stratosphere, especially for northern hemisphere winter-pole downwelling.
We parameterize subgrid-scale GWs in the Lagrangian ray-tracing scheme Multi-Scale Gravity-Wave Model (MS-GWaM) (Bölöni et al. 2021; Kim et al. 2021). MS-GWaM includes interactions between the GW field and the resolved flow, which are neglected in the traditional GW parameterization schemes. It has been implemented successfully into of the Icosahedral Non-hydrostatic (ICON) model in its upper-atmosphere configuration. Using the MS-GWaM output, we diagnose the sensitivity of the BDC using the downward-control principle.
How to cite: Masur, G. T., Kim, Y.-H., and Achatz, U.: The impact of subgrid-scale gravity waves on the Brewer-Dobson circulation, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15558, https://doi.org/10.5194/egusphere-egu23-15558, 2023.
Recently, high-resolution satellite instruments and general circulation models (GCMs) which resolve gravity waves explicitly are becoming available. However, because of their small temporal and spatial scales, the entire spectral range of gravity waves cannot be fully detected by global observations or simulated by a GCM. To enhance our understanding of the characteristics of gravity waves in the middle atmosphere, quantitative comparison between observed and model-simulated gravity waves is of great importance. The aim of this study is to make a quantitative comparison between gravity waves observed by the Atmospheric Infrared Sounder (AIRS) on NASA’s Aqua satellite and those simulated by a gravity-wave permitting GCM, named JAGUAR. As a nadir-viewing satellite instrument, AIRS has relatively high horizontal resolution varying from ~13.5 km to ~41 km and coarse vertical resolution of 7–20 km over the altitude range of 15–60 km. JAGUAR is a hydrostatic spectral GCM with a T639 triangular truncation. This model contains 340 layers from the ground to the model top of ~150 km with a constant log-pressure height interval of 300 m. We first applied a vertical filter simulating the observational filter of AIRS to the output data of hindcast simulations in the 2018/19 boreal winter performed with JAGUAR. Then, the filtered model data were resampled as AIRS observational granules. Gravity waves were extracted by subtracting a fourth-order polynomial fit in the cross-track direction of a granule, whose data length is 1780 km. A three-dimensional Stockwell transform was utilized to examine the amplitudes and wavelengths of dominant waves. Stratospheric gravity waves in the model results are compared with those in AIRS observations. It was shown that amplitude, zonal momentum flux, and meridional momentum flux of the gravity waves are in good agreement between the JAGUAR and AIRS data. These results support the validity of studies on gravity waves and their roles in the middle atmosphere by using the JAGUAR model. Peaks of gravity-wave amplitudes are observed along the winter eastward jet and summer westward jet. The peaks located in the former region got weaker, and the latter got stronger as the stratospheric sudden warming in January 2019 progressed. Compared to waves in the model data without the vertical filter applied, dominant waves in the filtered model data are half the amplitude in the regions where strong gravity waves are observed. This difference is most remarkable in eastern Eurasia, where the vertical wavelengths of dominant waves are relatively short. This fact implies the importance of careful consideration on the underestimation of wave amplitudes due to AIRS observational filter especially where waves having short vertical wavelengths are likely dominant.
How to cite: Okui, H., Wright, C., Hindley, N., and Sato, K.: Comparison of Stratospheric Gravity Waves in a High-resolution General Circulation Model with 3-D Satellite Observations, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-14145, https://doi.org/10.5194/egusphere-egu23-14145, 2023.
The momentum transport by orographic gravity waves (OGWs) plays an important role in driving the large-scale circulation throughout the atmosphere, which is subject to parameterization in numerical models. Current parameterization schemes commonly assume that the unresolved OGWs are hydrostatic, typically only valid for waves with large horizontal scale, weak winds and high stability. These schemes were originally developed for coarse-resolution numerical models and, as a result, captured the first-order effects of unresolved OWGs. With the increase in the horizontal resolution of state-of-the-art numerical models, unresolved OGWs are of smaller horizontal scales and may be more influenced by nonhydrostatic effects (NHE), thus challenging use of the hydrostatic assumption. Based on the analytical formulae of nonhydrostatic OGWs derived in our recent study, this work revises the orographic gravity wave drag (OGWD) parameterization scheme employed in the Model for Prediction Across Scales (MPAS) by accounting for NHE. Global simulations are conducted to investigate NHE on the momentum transport of parameterized OGWs and their impact on the simulated large-scale circulation. NHE are found to be the most evident in regions of complex terrain where the subgrid-scale orography is narrow. As NHE act to reduce the surface wave momentum flux (WMF) of OGWs, the revised scheme tends to inhibit wave breaking in the lower troposphere and transport more WMF upward, leading to an enhancement of OGWD in the upper troposphere and lower stratosphere. Over Antarctica, where the largest zonal-mean NHE occur, the OGWD-induced meridional circulation is strengthened, which helps reduce the cold pole and westerly wind biases associated with a too strong polar vortex, thereby alleviating the delayed breakdown of the Antarctic polar vortex in late spring and early summer, a bias commonly found in climate models.
How to cite: Xu, X., Zhang, R., Teixeira, M., van Niekerk, A., and Li, R.: A parametrization scheme accounting for non-hydrostatic effects on vertically propagating orographic gravity waves and implementation in the Model for Prediction Across Scales (MPAS), EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-13248, https://doi.org/10.5194/egusphere-egu23-13248, 2023.
Internal gravity waves (IGWs) are important distributors of energy and momentum in a stratified atmosphere. While most IGWs are presumably excited at lower altitudes their effects are most important between the upper troposphere and the mesopause (~85km). During propagating - both in the vertical and the horizontal - nonlinear IGWs can exert a wave drag on the large-scale winds, interact with the large-scale potential temperature, and influence transport and mixing of atmospheric constituents such as aerosols or greenhouse gases.
In state-of-the art weather and climate prediction models subgrid-scale IGWs are typically parameterized neglecting both the horizontal wave propagation (single-column assumption), the transient wave behavior including its effect on wave-mean-flow interactions (steady-state assumption) as well as time dependent wave generation. While being computationally efficient the missing physics, however, may lead to model errors and inaccurate predictions under varying boundary conditions. The potential importance of the horizontal wave propagation and wave transience has been shown in various theoretical, numerical and experimental studies.
The transient Multi Scale Gravity Wave Model (MS-GWaM) - implemented in the high-top model UA-ICON - aims to improve these shortcomings by allowing for transient and three dimensional wave propagation. The parameterization is based on a multi scale WKBJ analysis of the compressible atmosphere and includes various non-orographic wave sources, non-dissipative wave-mean-flow interactions as well as wave breaking. Internally, the parameterized gravity waves are treated as Lagrangian volumes with the dynamics prescribed by the well known gravity wave modulation equations. A suitable projection method of wave properties onto the unstructured model grid facilitates the calculation of wind and temperature tendencies. What is more, an efficient parallelization of the ray-tracing scheme allows for simulations in reasonable computation times, being much faster than corresponding wave resolving runs.
While satisfactorily reproducing the observed zonal-mean wind and potential temperature climatology the model results reveal new insight into the detail of the role of IGWs in the atmosphere. In particular, probability density functions of wave momentum fluxes exhibit the typical observed long tails (i.e. wave intermittency) which cannot be reproduced with steady-state parameterizations. Moreover, the three dimensional distribution of wave momentum and wave action fluxes differ greatly when relaxing the single-column assumption. As an example the well known three dimensional refraction of IGWs into polar jets can be shown.
How to cite: Voelker, G. S., Kim, Y.-H., Bölöni, G., Zängl, G., and Achatz, U.: MS-GWaM - A three dimensional transient parameterization for internal gravity waves in atmospheric models, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9196, https://doi.org/10.5194/egusphere-egu23-9196, 2023.
The Multi-Scale Gravity Wave Model (MS-GWaM) uses raytracing-based modelling that supports transient gravity-wave parametrisation. The state-of-the-art implementation of MS-GWaM in the upper-atmosphere ICON model solves the raytracing equations in three dimensions and accounts for background (non-orographic) and convective gravity-wave sources. Our work extends the capabilities of MS-GWaM to include orography gravity-wave sources, and we present methods and preliminary results towards this goal. Specifically, we first determine the spectral representation of the topography in each ICON grid cell via Fourier fitting. We then apply linear theory to obtain a representation of the bottom boundary for the raytracer. Finally, the bottom boundary serves as an initial condition for the raytracer-based parametrisation of orographic gravity waves. Preliminary results indicate that a judicious setup of this bottom boundary allows for an optimal tradeoff between computational efficiency and a sufficiently accurate representation of the underlying topography.
How to cite: Achatz, U., Chew, R., and Dolaptchiev, S.: Towards an implementation of topography in a next-generation gravity-wave parameterisation, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-1251, https://doi.org/10.5194/egusphere-egu23-1251, 2023.
Using a 3-dimensional (3D) Lagrangian ray-tracing approach, a realistic gravity-wave (GW) parameterization has been developed: Multi-Scale Gravity Wave Model (MS-GWaM). It is a unique and useful tool to simulate and study the 3D transient dynamics of GWs and their interactions with various meteorological phenomena. We implement MS-GWaM into the ICOsahedral Non-hydrostatic model (ICON) and conduct a simulation of the quasi-biennial oscillation (QBO). A particular focus of the study is on the effect of oblique propagation and transient dynamics of GWs on the simulated QBO dynamics. Source spectra of GWs in MS-GWaM are calculated online using the convective latent heat modeled by ICON's cumulus parameterization, as the QBO dynamics is sensitive to the source spectra. In the GW-source scheme a tuning parameter, the areal fraction of convective cells in a model grid cell, is used to produce a reasonable QBO period. In the simulation result, the amplitude of the QBO is realistic in the middle stratosphere but underestimated in the lower stratosphere. The easterly QBO wind is shorter in height than that of the observed QBO. It is notable that in the solstice seasons when the convective activity is maximal off the equator (~8°), GWs with relatively large horizontal wavelengths tend to propagate equatorward from the active convection region. This oblique propagation leads to an effective coupling between the GWs and the QBO. Another simulation is performed using the same experimental setup except that in MS-GWaM the horizontal propagation is neglected and the steady-state assumption is used, as in conventional GW parameterizations. The QBO in this simulation exhibits a large difference from that using the 3D transient MS-GWaM: The QBO has a much longer period (~4 years) and its easterly phase descends a bit less. QBO jets tend to form off the equator in the solstice seasons, centered on the latitudes of active convection.
How to cite: Kim, Y.-H., Voelker, G., Bölöni, G., Zängl, G., and Achatz, U.: Simulation of the quasi-biennial oscillation using a fully 3D transient gravity-wave parameterization, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-8145, https://doi.org/10.5194/egusphere-egu23-8145, 2023.
Gravity waves (GW) are one of the key drivers of middle atmospheric circulation. They drive the mesospheric circulation and the QBO - the predominant mode of tropical stratospheric variability - and play an important role in the wintertime polar vortex variability. These waves manifest over spatial scales as small as O(10 m) to as large as O(1000 km) and thus, are often poorly resolved in global climate models on account of limited model grid resolution and grid-scale numerical dissipation. Moreover, the parameterizations used to represent the momentum forcing associated with GW are highly idealized and often not well-tuned due to limited observations. These parameterizations simplify GW representation by ignoring certain aspects of their dynamical evolution, including lateral propagation, transience, and intermittency, which results in an inaccurate model representation of their interaction with the synoptic and mean flow.
The present work focuses on creating a new, data-driven emulator for GW representation in climate models. The emulator employs an artificial neural network that learns the local and non-local gravity wave evolution by training on high-resolution reanalysis (ERA5) and ECMWF’s global 1km-resolution climate model that respectively partly and fully resolve the mesoscale portion of the atmospheric gravity wave spectrum. We test the performance of the data-driven emulators by embedding them in an intermediate-complexity climate model and assessing their momentum contribution towards driving a suite of middle atmospheric processes including the springtime disintegration of the Antarctic polar vortex, the quasi-biennial oscillation of the tropical stratospheric winds, and the sudden stratospheric warmings.
How to cite: Gupta, A., Sheshadri, A., and Mansfield, L.: Non-local Machine Learning-based Gravity Wave Parameterization trained on an O(1 km) Resolution Global Climate Model, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11078, https://doi.org/10.5194/egusphere-egu23-11078, 2023.
Gravity waves have a variety of different sources including wind flow over mountains, convection and jet stream instabilities. Yet when working with observations of gravity waves we can only make informed guesses of their sources. In this work we use GROGRAT to backwards ray trace stratospheric observations of gravity waves globally to learn more about their origins.
We use observations of temperatures at 40km altitude observed by the AIRS (Atmospheric InfraRed Sounder) instrument on NASA’s Aqua satellite. From these observations we extract temperature perturbations and use the 3D Stockwell transform to derive gravity wave properties such as momentum flux, horizontal wavelength, vertical wavelength. These gravity waves are then backwards ray traced through the ERA5 atmosphere. The significance in this work lies in the volume: we ray trace 21 years (2002-2022) of AIRS data globally, representing by far the largest such observational dataset ever reverse ray-traced.
By investigating the lowest traceable altitude of these rays, we can attribute the gravity waves to their sources (orographic gravity waves will originate near the surface whilst convective waves will have a higher origin). We can also investigate the horizontal propagation of orographic gravity waves from specific mountain ranges and how this changes seasonally. This work aims to answer the question: “Where do gravity waves observed by AIRS come from?”
How to cite: Noble, P., Wright, C., Hindley, N., and Moffat-Griffin, T.: Ray-tracing global gravity wave observations in 21 years of AIRS data, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-8137, https://doi.org/10.5194/egusphere-egu23-8137, 2023.
Retrieving global observations of gravity waves (GW) from recent satellite missions is challenging. Nadir viewing satellites such as AIRS provide directional momentum fluxes, but lack fine vertical resolution and hence observe only those GW with exceptionally high intrinsic phase speed. Limb scanning instruments such as HIRDLS and SABER have only a single measurement track and hence provide only an estimate of absolute GW momentum flux. In addition, the sparse along-track sampling of these limb sounders introduce uncertainties in horizontal wavelength. GPS-RO can provide GW profile triplets, allowing in principle the horizontal direction of GW propagation to be inferred, but these triplets are rare. Finally, direct wind measurements from Aeolus are restricted in altitude to less than ~25km and only provide the wind component in the direction of the lidar beam from one observational track. In consequence, also Aeolus cannot reveal horizontal propagation direction and GW momentum flux.
This situation could be dramatically improved by bringing a limb imager into space. A limb imager combines the very dense spatial sampling of a nadir viewing instrument with the high vertical resolution of a limb sounder. This will provide an almost complete description of the vertical spectrum of GWs, necessary for inferring drag estimates. Such global GW momentum flux data would for the first time allow to retrieve a global momentum budget from the mid-troposphere to the upper mesosphere.
The changing-atmosphere infra-Red Tomography (CAIRT) mission candidate for ESA's earth explorer 11 proposes a limb imager for spatial sampling of 25 km across-track, 50 km along-track and 1 km in the vertical. From this we expect to infer directional GW momentum fluxes from the tropopause to 70 km or higher. This will allow longstanding scientific questions to be addressed such as the quantification of tropospheric GW sources and their related phase speed spectra and the identification of secondary wave generation in the stratosphere and lower mesosphere. Considering the momentum flux at higher altitudes, secondary wave generation competes with oblique GW propagation which allows GWs from low latitude sources to reach the high latitudes mesosphere and thus avoid critical levels. In general, two-way interaction with the background flow will be considered via the modulation of the GW spectrum by the winds and the mean wind accelerations by the GWs. In this contribution we will outline the CAIRT instrument concept, give an overview of the mission’s objectives and demonstrate its potential using simulated observations.
How to cite: Preusse, P., Polichtchouk, I., Osprey, S., Ungermann, J., Rhode, S., Chipperfield, M., Errera, Q., Friedl-Vallon, F., Funke, B., Godin-Beekmann, S., Hoffmann, A., Malavart, A., Raspollini, P., Sinnhuber, B.-M., Verronen, P., and Walker, K.: The CAIRT earth explorer 11 mission: a way towards global gravity wave momentum budgets, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12273, https://doi.org/10.5194/egusphere-egu23-12273, 2023.
Recent interpretations of atmospheric gravity wave propagation have emphasized the importance of secondary and higher-order gravity waves. One implication of multi-stage vertical coupling of gravity waves could be an increased probability of measuring larger vertical wavelengths than would be expected from a primary gravity wave. These secondary waves are also expected to be intermittent in time and localized in space, which means that lidars are an excellent technique for detecting these phenomena. We present lidar gravity wave measurements from temperatures and winds using a zenith pointing beam and two 25-degree off-zenith beams. In each lidar field-of-view, gravity wave energy is estimated as a function of vertical wavelength and period using a Morlet wavelet analysis. This analysis is conducted at multiple altitudes in each of the three beams to determine small-scale horizontal variability, which could indicate small-scale wave activity associated with primary wave breaking.
How to cite: Wing, R., Gerding, M., Baumgarten, G., Strelnikova, I., Franco-Diaz, E., and Mossad, M.: Investigation of Secondary Gravity Wave Variability using a 3-Field-of-View Doppler-Rayleigh Lidar in Kühlungsborn, Germany, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3226, https://doi.org/10.5194/egusphere-egu23-3226, 2023.
The polar night jet, i.e., the edge of the polar vortex, maximises in the altitude range of 30 km to 70 km. The polar vortex is known to affect even underlying layers and the weather. The polar night jet shows the highest mean wind speeds observed in the atmosphere and likely plays an important role in multi-step vertical coupling not only from the ground, but also from the upper atmosphere downward.
Direct measurements of the polar night jet’s extreme atmospheric motion are rare and limited to a few rocket soundings or locations with dedicated remote sensing techniques.
We operate lidar and radar instruments capable of measuring temperatures and winds above northern Norway (ALOMAR, 69°N) and northern Germany (Kühlungsborn, 54°N). The instruments have observed the atmosphere frequently inside and outside the Polar Vortex for more than 10 years.
Using lidar measurements of temperatures and winds allows for studying up- and downward-propagating gravity waves in complicated dynamical situations that are often found at the polar vortex edge. Observing simultaneously up- and downward propagating waves may indicate gravity wave breakdown as well as the generation of secondary gravity waves and turbulence. Turbulence is frequently detected using the MAARSY VHF radar. So called Polar Mesosphere Winter Echoes (PMWE) are observed if sufficient ionisation and turbulence exist.
We will discuss the relationship between waves, turbulence, and the polar vortex based on lidar and radar observations.
How to cite: Baumgarten, G., Franco-Diaz, E., Fiedler, J., Gerding, M., Latteck, R., Mossad, M., Renkwitz, T., Strelnikova, I., Strelnikov, B., and Wing, R.: Observation of Gravity Waves and Turbulence at the Polar Night Jet, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-14447, https://doi.org/10.5194/egusphere-egu23-14447, 2023.
Gravity waves are a major source of the middle atmospheric short-term variability. The Hunga Tonga-Hunga Ha‘apai volcanic eruption provided a unique opportunity to study gravity wave propagation around the globe from a well-defined source. The eruption triggered several atmospheric signatures including a lamb wave (troposphere/stratosphere/mesosphere) and a package of gravity waves. Here we present results of gravity wave signatures found in mesospheric winds leveraging multi-static meteor radar networks such as the Nordic Meteor Radar Cluster and CONDOR. We were able to identify the eastward and westward propagating gravity waves. Furthermore, it was possible to estimate the intrinsic wave properties such as a horizontal wavelength of approximately 1600-2000 km and an intrinsic phase speed of 200 m/s.
How to cite: Stober, G., Liu, A., Kozlovsky, A., Qiao, Z., Tsutsumi, M., Gulbrandsen, N., Nozawa, S., Lester, M., Belova, E., Kero, J., and Mitchell, N.: Gravity wave signatures in mesospheric/lower thermospheric winds caused by Hunga Tonga-Hunga Ha‘apai volcanic eruption identified by CONDOR and the Nordic Meteor Radar Cluster , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12882, https://doi.org/10.5194/egusphere-egu23-12882, 2023.
