D7.5: Report on the application hackathon with a focus on the importance of resolving meso and submesoscales

About this document Report on the application hackathon with an asseessment of the role of SR-ESMs in improving climate projections and providing input to international agreements (e.g. the Paris Climate Accord). The focus will be on the oceanic component, and on aspects such as the passive uptake of heat and carbon by the ocean. Work package in charge WP7 Executive summary The Hackathon was organized in March 2024 in Hamburg under the lead of the Storms and Oceans theme as a collaborative event together with the Horizon-Europe-funded EERIE and the German BMBF-funded WarmWorld projects. In addition to these projects, we welcomed a group from MPI-M and Hamburg University. This group works specifically on ocean biogeochemistry and the carbon cycle in the framework of the H2020 ESM2025 project and Hamburg University’s Cluster of Excellence CLICCS using the HAMOCC biogeochemistry module. The focus of the Hackathon was an assessment of the newly available NextGEMS Cycle 4 experiments in comparison with previous cycles and the EERIE simulations. During the preparation of the Hackathon intensive cooperation took place among the projects to ensure that the simulation data were in place ahead of time and that a comprehensive set of tools for data assessment and evaluation was available. NextGEMS simulations were made available via catalogues in the innovative HEALPix format that allows users to assess the data at different resolutions. The application Hackathon addressed the specific question whether it is important to resolve meso- and submesoscales in the ocean models in climate simulations. To include a larger community working on aspects of eddy-resolving models, NextGEMS joined forces with EERIE to assess the role of eddies in transient climate change simulations. Furthermore, in collaboration with the HAMOCC group the participants analyzed additional simulations with interactive ocean biogeochemistry that allowed the role of eddies and storms for air-sea exchanges to be investigated. In particular, the group studied the uptake/release of anthropogenic carbon at fronts or underneath cyclones and their role in triggering/damping phytoplankton blooms. Other topics pursued during the Hackathon followed the work schedule of the individual work packages in the Application Phase. A task-force concentrated on a bug in the sea-ice module of ICON and successfully eliminated a bug in the sea-ice ocean interface. The Storms & Society group conducted social network analyses on the participant’s interactions within the hackathons and continued their work on knowledge co-production and dissemination. Figure 1: The Cycle 4 hackathon participants in front of the Max Planck Institute for Meteorology in Hamburg