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W1: Gravity Wave Parameterization for the Atmosphere

Principal investigators: Prof. Ulrich Achatz (Goethe University Frankfurt), Prof. Carsten Eden (Universität Hamburg), Prof. Franz-Josef Lübken (Leibniz Institute of Atmospheric Physics)

Present-day approaches to parameterize mesoscale motions in atmospheric models are oversimplified and over-tuned and hence not sufficiently reliable. Neither gravity-wave (GW) transience nor GW horizontal propagation is taken into account, although there is mounting evidence that they play a significant role. We will resolve these issues by the extension of the Lagrangian spectral GW model (MS-GWaM) in the atmosphere model ICON-a by lateral propagation and by the implementation of the related IDEMIX-a closure into the same model. 
While MS-GWaM is based on the fully resolved spectral GW energy equation, the related IDEMIX approach is simpler, but for the same reason also more efficient. Moreover, progress in GW-resolving modelling, using a novel dynamic macro-turbulence parameterization based on the Smagorinsky model (DSM), and lidar measurements in subproject T1 suggested merging these activities into W1. Highly resolved model and lidar data will be used for the validation of the parameterization approaches.

The following core themes will be in focus:

  • Implementation of lateral propagation into MS-GWaM in ICON-a. Validation against lidar measurements and GW resolving simulations.
  • Implementation of IDEMIX-a into ICON-a, including also lateral propagation. Validation against MS-GWaM, lidar data, and data from GW-resolving simulations.
  • Extension of the DSM parameterization as a unified anisotropic closure scheme for atmospheric flows from the troposphere above the boundary layer to the upper mesosphere.
  • Lidar observations covering the complete range of temporal and spatial scales relevant for GWs and the transition to turbulence, for the validation of the parameterizations.

The recently proposed parameterization module "Internal wave Dissipation Energy and MIXing" (IDEMIX) describes the generation, propagation, interaction, and dissipation of the internal gravity wave field and can be used in ocean general circulation models to account for vertical mixing (and friction) in the interior of the ocean. It is based on the radiative transfer equation of a weakly interacting internal wave field, for which spectrally integrated energy compartments are used as prognostic model variables. IDEMIX is central to the concept of an energetically consistent ocean model, since it enables to link all sources and sinks of internal wave energy and furthermore all parameterized forms of energy in an ocean model without spurious sources and sinks of energy.

Gravity waves are an important part of the energy cycle of the atmosphere and exchange momentum and energy with the mean flow due to wave breaking and wave refraction. Wave breaking and the resulting mean-flow effects need special parameterization in global climate models as they usually resolve at most a small part of the full spectrum of gravity waves. In W1 we apply the IDEMIX concept to develop corresponding gravity wave schemes for atmospheric circulation models. We propose to base a new, energetically consistent gravity wave parameterization on the radiative transfer equation for a field of waves. This method is fundamentally different from conventional schemes which describe the superposition of monochromatic waves launched at a particular level and which make the strong assumption of a stationary mean flow. As for the ocean, the wave field is represented by the wave-energy density in physical and wavenumber space. This new concept goes far beyond conventional gravity wave schemes which are based on the single column approximation. The radiative transfer equation has – to our knowledge – never been considered in the atmospheric community as a framework for sub-grid-scale parameterization. The proposed parameterization will, for the first time, 1) include all relevant sources continuously in space and time and 2) accommodate all gravity wave sources (orography, fronts, and convection) in a single parameterization framework. Moreover, the new scheme is formulated in a precisely energy preserving fashion.

The IDEMIX concept was shown to be successful for ocean applications but instead of focussing on the mixing effect by breaking waves as for the oceanic case, the focus in the atmospheric application is on the wave-mean flow interaction, i.e. the gravity wave drag and the energy deposition. We will extend the concept of energetically consistent closures to atmospheric gravity wave closures. The project will contribute to a transfer of knowledge from the oceanic community to the atmospheric community and vice versa.

Report - Ocean Sciences 2026 in Glasgow by Michael Cox

At the end of February, TRR181 went on tour to Ocean Sciences 2026, the first big conference of the year. Where better to talk marine science than the thriving port city of Glasgow?

Our journey started in the wee hours in Hamburg. We numbered four – Pablo, Belal, Moritz and me. As we travelled, our numbers grew, and we soon had a gaggle of oceanographers in Amsterdam. We resisted the debauchery frequently embraced by my fellow Brits in the Dutch capital, opting instead for a stroll along the canals. Our ferry left in the early evening and we arrived in Newcastle the following morning.

There were blue skies over the cliffs of North-East England as we approached land. This is the closest I have ever come to a research cruise and I was delighted to see a grey seal in the harbour. My Nature paper on the sighting will be available shortly.

At Newcastle, we boarded the train for a picturesque journey along the Northumberland coastline up to Edinburgh. Upon arrival, I introduced our quartet to the Scottish breakfast roll, with haggis, black pudding and tattie scones. Later, Belal paid £8 to kiss an owl. The weather turned as we made our way to Glasgow but despite the rain, our spirits remained high. Belal looked wistfully out of the train window, yearning for his avian companion.

The opening reception for the conference was held in the Glasgow Science Centre which contained interactive exhibitions for Pablo and the other children in attendance. The grown-up science started the following day.

Project members Manita Chouksey, Han Wang, Friederike Pollmann and Pablo Sebastia Saez together convened four sessions on internal and surface gravity waves. There were two oral sessions, a poster session and an eLightning (digital poster) session. All were well attended and the science was riveting. A resounding success! Elsewhere, Nils Brueggemann chaired oral and poster sessions on energy transfers in turbulence, and Knut Klingbeil chaired sessions on the numerical challenges in ocean model development.

The programme ran from 8.30 am to 6 pm every day. In the evenings, we sampled the finest food and drink Glasgow has to offer. For example, we ate at a curry house with a gallery of famous guests on their walls including royalty and presidents. The waiter took an unexpected photograph of us and returned with a framed copy to commemorate our visit.

Somehow, Pablo and I found time in our busy schedule to visit the University of Glasgow alongside friend-of-the-TRR Gaspard Geoffroy. The buildings would have looked quite at home in a certain popular wizardry franchise. The campus houses the Hunterian museum, with an impressive collection of scientific equipment including a tide gauge and Lord Kelvin’s harmonic analyser. As tidal researchers, Gaspard and I found this thrilling.

On Thursday evening, we headed to a party hosted by Scripps oceanographers and watched senior professors get plastered to the tune of Chappell Roan’s Pink Pony Club. Afterwards our group split. Some people went into a basement bar to watch topless men play heavy metal, whilst Yang, Belal and I went to a corner shop and purchased a pint of milk.

After the previous night’s indulgences, it was impressive that we made it to the conference for 8.30 am the following day. As the talks drew to a close, we reflected on a successful week. We all felt enthusiastic to get back to Hamburg and start working on new ideas! For Pablo, Han and I, the fun wasn’t over. We would spend the following week hosted in Edinburgh by TRR181 Mercator fellow, Jacques Vanneste.

The highlights of our second week included visits to the National Museum of Scotland, walks up Arthur’s seat and Blackford Hill, and Pablo’s sensational talk in the Waves & Flows seminar series at the University of Edinburgh. Jacques hosted us for a delicious meal on our final night together. This generous hospitality was a fitting end to our time in the UK – an enjoyable and productive trip for everyone involved.

Research Stay in Lyon by Mohamed Mossad (Oct 23)

Exploring Atmospheric Dynamics

From the 1st of October and until the 14th, I had the opportunity to embark on a short research stay in Lyon, France, funded by the project TRR181 at École Centrale de Lyon. This period was not just a chance to collaborate and learn but also a stepping stone in my understanding of atmospheric dynamics, particularly regarding gravity wave (GW) spectra.

My time in Lyon was spent working alongside Raffaele Marino (scientist at CNRS, France) and the team at the Laboratory Mechanical Des Fluides Et D'acoustique (LMFA). The environment at LMFA was not only academically stimulating but also warmly welcoming, fostering both professional growth and personal connections.

One of the most enlightening aspects of this visit was the shift in my perspective on the processes which contribute to the canonical GW spectra. Discussions about turbulence and the scaling of gravity wave spectra opened my eyes to the broader physics underlying these phenomena. It was a transition from focusing merely on the slope of gravity wave spectra to understanding the vast, open-ended field of their scaling.

A highlight of my stay was exploring the relationship between the Froude number and statistics (kurtosis) of velocity and temperature fields. Although time constraints didn’t allow for its application on lidar data, the concepts presented were inspiring and thought-provoking.

Our work concentrated on validation of spectra from direct numerical simulations (DNS) against lidar data, scrutinizing how different wind regimes affect GW spectra. This involved a detailed comparison of integrated kinetic energy/scalar spectra with lidar data.

Leaving Lyon, I am armed with an array of studies and topics to delve into, especially regarding the comparison with DNS regimes. These studies are pivotal in enhancing our interpretation of GW data from lidar measurements. I am optimistic about the continuation of this collaboration in the future and the potential for significant findings.

Beyond the academic realm, Lyon itself proved to be a delightful experience. The city's transportation system was notably efficient which made commuting a breeze. The streets of Lyon are filled with friendly faces, many of them young students, also the 2023 Rugby World Cup was taking place there which added a lively and diverse vibe to the city. École Centrale de Lyon, nestled in this vibrant environment, struck me as an exceptional place for study and research, providing many chances to do sports as well.

I extend my deepest gratitude to the entire team at LMFA for their hospitality and support. Special thanks go to Rafaello Foldes and Fabio Feraco (IAP) for their invaluable help in answering my questions and assistance with data provision.

My research stay in Lyon was not only productive but also immensely rewarding. It has broadened my understanding and has surely impacted my approach to atmospheric science. I am grateful for this experience and hopeful that my contributions, though a fraction, have added value to our collective research endeavors.