The role of coherent air streams in shaping the Gulf stream’s impact on the large-scale extratropical circulation

• Applicant: Dr. Julian Quinting, since 10/2023
• Subject Area: Atmospheric Science
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 452248368

The variability of large-scale weather conditions in the North Atlantic region is dominated by quasi-stationary, persistent, and recurrent flow patterns. These so-called weather regimes are characterised by the occurrence of low- and high-pressure systems in specific subregions. Successful weather forecasts on time ranges of several days to a season (the sub-seasonal to seasonal – S2S – time range) rely on the correct representation of the life cycle of weather regimes in numerical models. Thereby, the maintenance of favourable conditions for the intensification of low pressure systems along a confined storm track and the initiation and maintenance of stationary high-pressure systems (atmospheric blocking) downstream, are thought to be key elements. There is increasing evidence that air-sea interaction especially along the Gulf Stream oceanic front, latent heat release in cyclones, and the advection of cold air masses from the Arctic play a key role for the variability of the large-scale circulation over the North Atlantic and Europe. Yet, the mechanistic understanding of how the associated air mass transformations over the ocean affect the large-scale flow is still limited. Furthermore, the relevance of these processes for the life cycle of weather regimes has not yet been established. In this challenging, three-year collaborative project at KIT and ETH Zürich, we aim to develop a integral view on the role of air-sea heat exchanges and diabatic processes in the Gulf Stream region in shaping large-scale flow variability over the North Atlantic and Europe. For that purpose, we will develop sophisticated Lagrangian air mass diagnostics combined with novel energetics diagnostics to investigate the evolution of weather regime life cycles and transitions between them with state-of-the-art high-resolution numerical data sets and own numerical simulations. Specifically we aim to combine our expertise in the dynamics of the large-scale circulation and weather systems, air-sea interaction – especially during cold air outbreaks – and the Lagrangian analysis of atmospheric processes to (i) obtain a mechanistic understanding of how air mass transformations along the Gulf Stream front influence the large-scale flow downstream with a focus on the formation and maintenance of blocking anticyclones, (ii) constrain the importance of storm-induced air mass transformations and diabatic processes for the maintenance of favourable conditions of cyclone intensification during regime life cycles and storm clustering, (iii) combine these insights into a unified and quantitative perspective on the processes shaping the role of the Gulf Stream for large-scale flow variability, and (iv) evaluate the representation of these processes in state-of-the-art numerical models. The proposed fundamental research will inform the improvement of numerical weather prediction and climate models.

• DFG Programme: Research Grants
• International Connection: Switzerland
• Partner Organisation: Schweizerischer Nationalfonds (SNF)
• Cooperation Partner: Dr. Lukas Papritz
• Ehemaliger Antragsteller: Professor Dr. Christian Grams, until 9/2023