Extratropical cyclones are a major control of weather and climate in the midlatitudes. Climate model simulations have been used to analyze the influence of global warming on extratropical cyclone dynamics. This study addresses the still open questions of whether cyclones will become more intense, what dynamic processes are responsible for these changes, and how this could impact the North Atlantic region. This study investigates extratropical cyclone dynamics over the two periods 1990-2000 and 2091-2100 using the Community Earth System Model Large Ensemble (CESM-LE) dataset. We analyze the storm response in the extended winter and summer seasons in the North Atlantic (NA) region. A Lagrangian cyclone detection is used to analyze the occurrence and spatial distribution of storm tracks. The evolution of cyclonic structures in a warming climate is studied with cyclone-centered composites. Likewise, a potential vorticity (PV) perspective is adopted to study the changes in the cyclone wind field near the surface. A trajectory analysis illuminates the contribution of diabatic processes to future changes of cyclone-associated PV anomalies. Firstly, through comparison with ERA-Interim reanalysis data, we find that the CESM-LE captures the current spatial distribution of intense cyclones adequately. Robust changes in cyclone occurrence and properties are found in the NA region for the end of the century. For instance, cyclone frequency decrease in a warming climate, whereas precipitation intensity increases. Projected intensity changes are generally small. Secondly, the structure of those cyclones whose intensities fall within the 90th percentile is studied via a composite analysis. Winter storm tracks of these most intense cyclones respond to climate warming with an eastward shift. This shift increases the risk of strong winds and extreme precipitation in western Europe. In winter, extratropical cyclones also exhibit structural changes that amplify precipitation intensity downstream and low-level wind flow to the southeast of the cyclone center. In present-day climate, PV inversion reveals the relevance of upper-level PV anomalies for contributing to the poleward wind flow to the east of the cyclone center. The simulated future intensification of this poleward flow is related to a strengthening of the low-level PV anomaly associated with amplified diabatic heating in combination with a dipole change in the upper-level PV anomaly pattern. Furthermore, a Lagrangian trajectory analysis is adopted to explicitly identify changes in air mass advection that result in the PV anomalies at lower and upper levels. At upper levels, the decreased PV anomaly to the south of the cyclone center results from a combined effect of a decreased climatological PV in the NA region and a shift in the origin of the air masses. Increased diabatic heating along backward trajectories leads to an amplification of positive PV anomalies near the cyclone center at both lower and upper levels. Finally, a scaling method is used to analyze the dynamic and thermodynamic contributions to cyclone-related precipitation changes on a storm-scale for the 10% most intense cyclones. Thermodynamic contributions dominate the precipitation increase over the coma-shaped main area of precipitation, while changes in the vertical wind (dynamic) contribute to enhanced frontal precipitation and a weakening of the precipitation to the west of the cyclone center. In conclusion, diabatic processes, specifically enhanced latent heat release, will primarily shape the anatomy of intense extratropical cyclones in the North Atlantic region in a warming climate. Therefore, a better representation of the diabatic process in climate simulations can help to constrain better the future dynamics of intense cyclones and their social impacts.
