My mission is to develop data analysis from our observations and apply it to the output from the Kühlungsborn Mechanistic Circulation Model (KMCM).

It is unrealistic to expect the numerical models to exactly simulate the real atmosphere for all observed penomena since the atmospheric flows are turbulent in nature.

My task is to extend the recently developed parameterization for friction/diffusion for atmospheric flows to the middle atmosphere.

I am a PhD student at the University of Hamburg and a member of the Collaborative Research Centre TRR 181 Energy Transfers in Atmosphere and Ocean (sub-project T2: Ocean Surface Layer Energetics). From the 29.06.2026 to the 03.07.2026, I participated in the third workshop of the trimester programme Mathematical Developments in Geophysical Fluid Dynamics, entitled Idealised Mathematical Models for Geophysical Flows, held at the Institut Henri Poincaré in Paris.

After attending the introductory school at the CIRM in Marseille in April, near the beautiful site of the Calanques, I went to Paris to participate in the third workshop of this programme.

I was particularly pleased that this workshop was held in Paris, as it was an opportunity to see some of my old friends from the Master's programme at Sorbonne University and to come back to this city to which I am particularly attached.

The third workshop lasted one week and took place at the Institut Henri Poincaré, in the Latin Quarter of Paris, which is well known for its intellectual and student atmosphere. We were sitting in the Charles Hermite amphitheatre, one of the oldest lecture halls of the institute, which has hosted many renowned mathematicians and physicists.

During this workshop, I attended many talks and presented my poster on an attempt at deriving the $\alpha$-modified Craik–Leibovich equations using geometric generalised Lagrangian mean theory. This work aims to develop a mathematical model describing wave–mean current interactions while accounting for the effects of turbulence through an $\alpha$-regularisation. Because the poster combines ideas from Craik–Leibovich theory, $\alpha$-models of turbulence and geometric GLM, it attracted researchers with rather different backgrounds, including oceanographers, applied mathematicians and specialists in mechanics. These discussions helped me to better identify which aspects of the work are the most accessible to different audiences and which questions naturally arise from each community.

I was very happy to see that this subject raised the interest of many people; it encouraged me a lot to continue. As the poster was displayed throughout the whole week, it also enabled me to continue discussions with people afterwards. This experience also highlighted the importance of poster sessions for presenting ongoing work, receiving feedback and establishing new scientific contacts.

Although the event in Paris was completely free of charge, lunches were organised directly next to the amphitheatre, which greatly facilitated discussions and informal interactions. One of the highlights of the week was undoubtedly the cocktail on the rooftop of the Maison Poincaré, where discussions continued in a relaxed atmosphere. Participants were also offered free admission to the Maison Poincaré's mathematics museum. I visited it with a few other participants and enjoyed discovering its interactive exhibitions.

The scientific programme covered a broad range of themes. The talks ranged from reduced models for strongly stratified turbulence, derived using asymptotic analysis, to the treatment of boundary conditions in wave–structure interactions. They showcased a variety of mathematical tools, including turbulence modelling, asymptotic methods, geometric mechanics, and numerical simulations. Although the topics were diverse, they all shared the common objective of improving our understanding of the fundamental mechanisms governing geophysical flows. At this stage of my PhD, this workshop helped me better understand how my research fits within the broader field of geophysical fluid dynamics.

In the following week, there will be a satellite conference, *Perspectives and Challenges in Geophysical Fluid Dynamics*, at the École normale supérieure. I am looking forward to meeting other members of the TRR and many other researchers there.

The workshop also gave me the opportunity to learn about future events of the community. Several participants recommended the Advanced Summer School on Mathematical Fluid Dynamics in Cargèse next year, which I hope to attend.

Jabeen Safeer, a PhD student at the University of Hamburg, attended the 57th International Liège Colloquium on Ocean Dynamics at the University of Liège in Belgium at the end of May. Here she shares her experiences.

The Liège Collocuium on Ocean Dynamics is one of the longest-running series in physical oceanography, bringing together leading researchers from across the globe to advance the understanding of ocean dynamics. This year’s colloquium revisited submesoscale dynamics of the ocean - a decade on from the 48th Colloquium in 2016 - taking stock of new developments across a range of oceanographic disciplines, including observational, modelling, and theoretical approaches. I was accompanied by Evridiki Chrysagi - my supervisor and also a TRR 181 member - and Arooba Nawaz, a master’s student at the Universität Hamburg.

We reached the city on the afternoon of May 24th and were greeted by the sight of the transparent, monumental vault of the Gare de Liege-Guillemins, built entirely out of glass and steel. The conference venue was the University of Liège's lecture hall, with neoclassical walls inscribed with the exceptional heritage of Wallonia, the French-speaking region of Belgium. The conference started with a session on remote sensing of submesoscale dynamics, which shed light on ongoing efforts to utilise high-resolution SWOT satellite data to reconstruct various ocean variables. Following the scientific sessions, we participated in a hands-on training session hosted by EUMETSAT (European Organisation for the Exploitation of Meteorological Satellites), focused on monitoring submesoscale ocean processes using Earth observation data. It provided us with new information and tools to work directly with freely available satellite-derived ocean data from the Copernicus Marine Service. The poster presentations were scheduled for the second day, along with an icebreaker event. Besides, the posters were on display all week, which provided me with a very relaxed environment to talk about my poster and discuss my work with several people. The remaining days featured keynote talks on frontal instabilities, wave-front/eddy interactions, multiscale processes, submesoscale dynamics at the boundaries and physical-biological interactions. I found it fascinating to learn that polar oceanographers use seal-borne CTD sensors to study Southern Ocean dynamics. This was just one example that highlighted for me how essential creativity is in conducting meaningful scientific research, as I discovered many throughout the colloquium.  Although the five days were packed with talks and activities, I found each talk to be very informative and gained several insights relevant to my own research. Outside of the scientific sessions, we spent our evenings walking through the beautiful streets of Liège and sampling a variety of local restaurants. The most delicious culinary experience we had was in an Afghan restaurant. The renowned Liège waffles also warrant a special mention. I am grateful to TRR 181 for supporting this trip, and to Evridiki and Arooba for the company, both in the lecture hall and our evening explorations of Liege.

Our goal is to resolve the small-scale processes that dominate the energy exchange as well as to identify the individual mechanisms as a function of the wind wave conditions.

Hello everyone, my name is Malte Loft and I work on the ”T4 Surface Wave-Driven Energy Fluxes at the Air-Sea Interface” subproject as a PhD student at the Hamburg University of Technology (TUHH).

I studied dual mechanical engineering at the Hamburg University of Applied Sciences and specialised in fluid mechanics at the University of Rostock as part of a Master’s degree. In September 2021, I started my PhD to investigate the energy fluxes at the air-sea interface using high-resolution CFD simulations (WP2).

Our goal is to resolve the small-scale processes that dominate the energy exchange as well as to identify the individual mechanisms as a function of the wind wave conditions, e.g. the wave age or wave slope of the current sea state. Due to mostly very high Reynolds numbers, it is hardly possible to perform Direct Numerical Simulations (DNS). Therefore, a hybrid turbulence model (Detatched Eddy Simulation, DES) is used for our simulations. First, a numerical wind-wave tank is developed to reproduce relatively simple laboratory conditions and to validate the numerical model with experimental results (WP1). In the animation shown, a non-linear surface wave can be seen propagating from left to right, involving strong wind forcing. Air separation events and highly turbulent structures are clearly visible. Due to our fully coupled model, we are able to extract the pressure fields and surface stresses at any point in space and can also include the influence of surface tension effects in our investigations. Furthermore, we produce large amounts of data during our simulations in order to determine phase-averaged quantities using triple decomposition. In other words, fields of pressure or velocity that correlate with the respective sea state, detached from turbulent fluctuations. With all this data, we hope to gain deep insights into the physical processes that determine the mechanical energy flow at the air-sea interface.

In the future, we will extend the application of our model to more complex scenarios, e.g. to highly non-linear sea states of the Baltic Sea, including further phenomena such as wave breaking. Another goal is to formulate the findings into improved parameterisations, in particular to improve the boundary conditions of current ocean models (WP3).

Here you can see a short video.

Last year I was asked if I would like to participate in a wind-wave project at the Alfred C. Glassell, Jr. SUSTAIN Laboratory in Miami, USA, for three weeks. After listening to the song "Miami" by Will Smith several times, I felt well prepared and started organizing the trip, especially the funding by the TRR. The wind-wave tank is top-notch, and I was very excited when everything was approved. After my arrival, I met the scientists from Columbia University, U.S. Naval Research Laboratory, University of New Hampshire, and of course University of Miami. From now on, we spent almost every day in the dark lab with no daylight – thanks to the Particle Image Velocimetry measurements. Outside it was summer and mosquito season, so we did not complain much. We survived working on weekends with strong Cuban coffee (do you really want the real one and no sleep for a week?). But the experimental work did not only take place in the lab; discovering the great dive sites of Miami was also part of my tight schedule. Shortly before my return flight, we cooled the tank, whereupon it began to leak as all the silicone seals contracted. This reminded me of the rainy weather in Hamburg, and I knew it was time to come home. I am very grateful for this experience and would recommend everyone not miss the opportunity to do a research stay.