L4: Multiscale Ocean-Atmosphere Coupling

My name is Henning Franke and I am a Postdoctoral Researcher in subproject L4 „Multiscale Ocean-Atmosphere Coupling“ at the Max Planck Institute for Meteorology (MPI-M). My scientific work focuses on better understanding the role of small-scale heterogeneity of the sea surface temperature in driving convective precipitation over tropical oceans. My main tool for addressing this research topic are numerical simulations with global km-scale coupled ocean-atmosphere models, in particular the ICON model from MPI-M. Since km-scale models are still a fairly new type of climate model, an extensive exchange with other modeling groups that are active in this field is essential for making progress. This is the reason why in November 2025 I joined a group of scientists from the MPI-M on a research trip to Japan.

The Japanese atmospheric research community under the leadership of Prof. Masaki Satoh from the Atmosphere and Ocean Research Institute (AORI) of the University of Tōkyō is a global pioneer in developing and using km-scale global climate models. In order to deepen the collaboration between AORI and MPI-M in developing and applying km-scale climate models, Prof. Satoh and Prof. Bjorn Stevens from MPI-M organized a two-day workshop at AORI. The workshop was further attended by researchers from the National Taiwan University (NTU) and Monash University in Melbourne. During the workshop, the main task for me and other participants was to develop ideas for the scope, the format, and the topics for a more in-depth collaboration between the participating institutions. As a starting point for these discussions, early-career researchers gave a short scientific presentation. These presentations gave an impressive overview of the breadth of research topics related to km-scale climate models that are addressed by the participating institutions. To deepen the connections made at the workshop, the workshop also left time for a Ping Pong tournament, a football game, and a hike to Mount Tsukuba. Especially the hike to Mount Tsukuba was a great experience and I really enjoyed the beautiful Japanese nature.

After three nice days at AORI, me and my colleagues from MPI-M moved on to Morioka, a small town in the north of Japan’s main island Honshu. Here, the 7th International Workshop on Nonhydrostatic
modelling (WS-NHM) took place, which was followed by a one-day meeting on coordinated experiments for km-scale climate model intercomparison. The WS-NHM is one of the
major conferences for the km-scale climate modeling community and as such a great possibility to present some of my research results. It further offered plenty of possibilities for exchange with
colleagues and gave a great overview of the latest progress in the field. This valuable input stimulated some new ideas for my research that I plan to test when I return to Hamburg.

However, my stay in Japan was a great experience also beyond scientific input and exchange. Daily dinners offered plenty of possibilities to delve into the amazing Japanese cuisine, which is much more than just Sushi and Ramen. My personal favorite is Okonomiyaki, a savory pancake which blends cabbage and other choosable toppings, and I highly recommend everyone to try it once in Japan! Furthermore, I learned a lot about the Japanese culture and the Japanese way of life in general. For example, I was not aware of the rich Japanese bath culture before my trip, but after my first visit to a traditional onsen (a natural hot-spring with a water temperature of around 40°C) I immediately understood why most Japanese love this tradition since centuries. By combining my research trip with some days of vacation, I was also able to visit Kyōto, often considered as Japan’s cultural center, as well as Tōkyō, Japan’s capital with its countless skyscrapers and modern overstimulation. Overall, I had a great time in Japan and I hope that I will be able to visit this amazing country again at some point in the future.

At this point, I would like to thank Prof. Dr. Masaki Satoh for organizing a very pleasant and interesting stay at AORI, as well as the organizers of WS-NHM for organizing such a great conference in Morioka. Furthermore, I would like to thank the TRR181 for providing the funding for this trip. I am very grateful for this research trip to Japan and would encourage other early-career researchers to seize similar opportunities.

At the end of last year, I spent two months in Perth, Western Australia, to work on a collaborative project with Jen-Ping Peng, who was a PhD in TRR181’s first phase and is now a PostDoc in the working group of Nicole Jones at the Indian Ocean Marine Research Centre of the University of Western Australia. For the most part, my stay in Perth was covered by the Australia–Germany Joint Research Cooperation Scheme, with the TRR kindly providing some additional financial support. The above scheme is an initiative of Universities Australia and the German Academic Exchange Service (DAAD) for the support of international academic cooperation. Early-career researchers from Australia and Germany are encouraged to hand in proposals for a joint research topic, and, if approved, the grant covers the expenses for a research stay at the partner institute. For our project, Jen-Ping and I decided that we want to combine our two fields of research and investigate the interactions of diurnal warm layers, submesoscale fronts and other turbulent processes in the surface mixed layer. For this, we firstly extended the 1D turbulence model GOTM to include 3D frontal effects and validated our model results by comparing them to published LES studies. Then, we used our model to recreate measurements taken previously during two campaigns in the Baltic Sea and the Indian Ocean and use the results to understand the governing processes involved. We found nice agreements between the measurements and our simple model and are planning on publishing two joint papers on these topics.

But besides the work aspect, Western Australia was also a great place to explore and spend time. Jen-Ping was an excellent host (I think we went to every great Asian restaurant in all of Perth) and the weather was pleasant from beginning to end (basically nothing but sunshine for two months). I stayed in a researcher accommodation on campus, which is located a few kilometres away from the city centre directly at the Swan river estuary with lots of green areas and beautiful old trees. Moreover, I got to go on two nice road trips up and down the coast, explore the Margaret River wine region, see quokkas on Rottnest Island and snorkel in the beautiful Ningaloo Reeve national reserve with an infinite amount of fish, stingrays and even a big sea turtle. I also got to see a living colony of stromatolites, microorganisms that are believed to be the oldest form of life on earth dating back 3 billion years, and that can only survive in hypersaline estuaries like Shark Bay in Western Australia. And while there were a few snake and spider sightings, I didn’t have the heart to look up their level of toxicity, so I like to believe it was all safe and sound.

I can definitely recommend looking into the Joint Research Cooperation Scheme (it exists not only between Germany and Australia, but also other countries) and would strongly encourage others to take the opportunity to extend their network and travel, maybe to Perth, it’s a lovely corner of the world. I would like to thank Jen-Ping, Nicole Jones and all other members of this working group for hosting me, showing interest in my research and teaching me about their fields of research.