What favours the midlatitude survival of cyclones of tropical origin (CTOs)?

Cyclones of tropical origin (CTO) occasionally propagate to the midlatitudes, posing a significant hazard to regions that are unaccustomed to hurricane-force winds and extreme precipitation. Notable examples of CTOs that have significantly impacted Europe are Ophelia (2017), Lili (1996), and Leslie (2018). Given the rarity of these types of CTOs, the physical mechanisms that influence their formation, motion, and extra-tropical transition are poorly understood, complicating predictability and disaster risk response. In particular, the processes that enable the survival of CTOs in the midlatitudes are highly uncertain. Previous studies have suggested that the steering and intensification of CTOs is strongly modulated by the interaction with the background atmospheric circulation, but evidence is limited to few remarkable historical examples. In this study, we leverage ensemble hindcasts to construct a large, physically consistent set of plausible CTO events originating in the Atlantic Ocean that recurve eastward and reach the midlatitudes. Secondly, we apply a trough detection algorithm (Schemm et al. 2020) to investigate whether the interaction between cyclones and troughs plays any role in favouring or inhibiting CTO survival in the midlatitudes. The large volume of data provided by ensemble hindcasts is crucial for reducing uncertainty and advancing our understanding of the processes that may lead to CTO impacts in Europe, including how these processes may evolve under anthropogenic forcing.