Extra-tropical Transition of Tropical Cyclones in the PRIMAVERA Simulations

Abstract

In this study, the simulations of six PRIMAVERA high-resolution climate models (CMCC-CM2-VHR4, CNRM-CM6-HR, EC-Earth3-HR, ECMWF-IFS-HR, HadGEM3-GC31-HM, MPIESM-1-2-XR) were analysed in terms of their capability to resolve the extra-tropical transition (ETT) of tropical cyclones (TC) towards Europe and the potential generation of warm seclusion storms. All models exhibit a good response in reproducing the above mentioned processes apart from CMCC-CM2-VHR4 and MPIESM-1-2-XR. This result is mainly attributed to data limitations for the former model, but possibly to a poor performance for the latter model. CNRM-CM6-HR and HadGEM3-GC31-HM generate a higher than normal number of tropical cyclones in general whereas EC-Earth3-HR and MPIESM-1-2-XR generate a lower number. Concerning the number of tropical cyclones that arrive in Europe, CNRM-CM6-HR and HadGEM3-GC31-HM are the only models simulating a realistic value. In general, no distinct preferable genesis region for the systems that reach Europe was observed however, the systems which additionally transform into warm-seclusion storms originate from the western tropics. A striking feature is the large number of weaker systems tracked in the data as well as the earlier tracking of the cyclones in time. An explanation for this behaviour is the performance of the tracking algorithm in conjunction with the PRIMAVERA data, however further examination is required. The Hart-phase diagrams for all models, apart from MPIESM-1-2-XR and CMCC-CM2-VHR4, demonstrate the typical evolution of these systems that reach Europe, beginning from the tropical stage to extra-tropical, to warm seclusion and then to decay. The same models simulate more than or close to 50$\%$ of the systems that arrive in Europe to be warm-seclusion storms which also acquire the highest intensity. The comparison with re-analysis data reveals similar features for the pressure although it displays small discrepancies concerning the genesis regions and the frequency of the TCs that reach Europe. Last but not least, the warm seclusion structure is not resolved in one of the re-analysis datasets.