Future changes in the extratropical storm tracks and cyclone intensity, wind speed, and structure

This is the final version. Available on open access from Copernicus Publications via the DOI in this record. Data availability. ERA5 reanalysis is available from the Copernicus Climate Change Service Climate Data Store (https://doi.org/10.24381/cds.bd0915c6, Hersbach et al., 2018). CMIP6 data are publicly available through the Earth System Grid Federation (Eyring et al., 2016).Code availability. Code is available at the request of the author. The cyclone tracking and compositing algorithm TRACK is available at the request of Kevin Hodges from https://gitlab.act.reading.ac.uk/track/track (Hodges, 2022, 1994, 1995, 1999)Future changes in extratropical cyclones and the associated storm tracks are uncertain. Using the new CMIP6 models, we investigate changes to seasonal mean storm tracks and composite wind speeds at different levels of the troposphere for the winter and summer seasons in both the Northern Hemisphere (NH) and Southern Hemisphere (SH). Changes are assessed across four different climate scenarios. The seasonal mean storm tracks are predicted to shift polewards in the SH and also in the North Pacific, with an extension into Europe for the North Atlantic storm track. Overall, the number of cyclones will decrease by ∼5 % by the end of the 21st century, although the number of extreme cyclones will increase by 4 % in NH winter. Cyclone wind speeds are projected to strengthen throughout the troposphere in the winter seasons and also summer in the SH, with a weakening projected in NH summer, although there are minimal changes in the maximum wind speed in the lower troposphere. Changes in wind speeds are concentrated in the warm sector of cyclones, and the area of extreme winds may be up to 40 % larger by the end of the century. The largest changes are seen for the SSP5-85 scenario, although a large amount of change can be mitigated by restricting warming to that seen in the SSP1-26 and 2-45 scenarios. Extreme cyclones show larger increases in wind speed and peak vorticity than the average-strength cyclones, with the extreme cyclones showing a larger increase in wind speed in the warm sector.Natural Environment Research Council (NERC