Abstract/Summary

Post-tropical cyclones (PTCs) can bring extreme winds and heavy precipitation to Europe. This thesis aims to further our understanding of the hazards posed to Europe by PTCs, and the factors (environmental and cyclone-specific) governing their development, variability, and projected changes. It is shown that PTCs are disproportionately responsible for windstorm risk over Europe: Despite comprising less than 1% of the cyclones impacting Northern Europe during the North Atlantic hurricane season, approximately 9% of the cyclones impacting the region during the hurricane season with storm-force (>25 m s -1 ) winds are PTCs. The interannual variability of recurving North Atlantic tropical cyclones (TCs) – defined as TCs which reach the North Atlantic midlatitudes – is shown to be governed by TC activity in the Main Development Region and subtropical North Atlantic, with interannual variability in the seasonal mean steering flow playing a smaller, secondary role. PTCs which are stronger at their TC lifetime maximum intensity, or which reintensify after ET, are shown to be significantly more likely to reach Europe. Europeimpacting PTCs interact more strongly with an upstream trough in a more baroclinic environment and often reintensify upon crossing a midlatitude jet streak. Future projections of PTCs in five CMIP6 models are shown to capture many of the observed features of the TC and PTC climatologies in the North Atlantic, and the disproportionate risk associated with Europe-impacting PTCs. No robust 21st century change in Europe-impacting PTC frequency or intensity is found in these models, because two competing factors – a decrease in North Atlantic TC frequency, and an increase in the fraction of TCs reaching Europe – are of the same magnitude. This thesis provides a framework to understand the European PTC climatology and provides evidence of an uncertain future for European PTC risk.