INTERACT

Abstrakt: Wider research context: Weather fronts are an important meso-scale link between large scale and regional weather, and are closely linked to extreme weather events. Fronts are embedded into, and interact with large-scale weather systems such as cyclones, which themselves are influenced by largescale drivers and modes of variability. Examples of such drivers are the temperature gradient between subtropical and polar airmasses, patterns of sea surface temperature and sea ice concentrations, the polar vortex and sudden stratospheric warmings. Climate change affects the large-scale drivers of fronts. Moreover, changes in large-scale climate and weather may change the character of fronts themselves, and as a consequence also the associated extreme events. The vast range of relevant scales makes the simulation of extreme events associated with fronts a challenging task, and climate models in fact have deficiencies at all these scales. To understand the response of extreme events to global warming, it is therefore crucial to assess how well the relevant processes and their interactions are simulated, and how model deficiencies affect projections of extreme events.

Research questions: Despite their relevance for extreme events, research on fronts in a changing climate is only an emerging topic. The main aim of INTERACT is to understand the role of fronts in scale interactions that shape extreme events in a changing climate. To address this aim, INTERACT will answer the following research questions in collaboration with two Russian partner institutions:
1. How are regional extreme events associated with fronts controlled by the internal variability and interaction of planetary-scale, synoptic-scale and meso-scale frontal dynamics?
2. How realistically are these phenomena, their interaction, and their influence on extreme events simulated by a hierarchy of climate models, included added value of high resolution?
3. How do these phenomena, their interaction and thus the related extreme events change in a warming climate?

Approach: To answer these questions, INTERACT will conduct global climate model sensitivity simulations, simulations of selected target regions with very-high resolution regional climate models, and simulations of individual extreme events under present and future climatic conditions; diagnose cyclones and fronts in observations and a hierarchy of climate model simulations; develop new diagnostic tools; evaluate climate model performance based on process-understanding; and assess the influence of climate change on the processes shaping extreme events associated with fronts.
Level of innovation: INTERACT will employ a hierarchy of new model ensembles, apply novel processes-based diagnostics, and use innovative approaches to explore uncertainties, to improve our process understanding of extreme events in a changing climate, and thus to increase the credibility of projections of weather extremes. INTERACT will contribute to international initiatives such as HighResMIP, CORDEX-FPS Convection and DAMOCLES, the WCRP Grand Challenge on Extreme Events and to the understanding of future weather. Primary researchers involved: Douglas Maraun (University of Graz) and Vladimir Semenov (Obukhov Institute of Atmospheric Physics, Moscow).