Comment on wcd-2022-62

Abstract

Extra-tropical cyclones (ETCs) are the main cause of precipitation in the mid-latitudes and there is substantial evidence that ETC-related precipitation will increase in the future. However, little is known about how this will impact on the dynamical strength of ETCs, and whether the impact will differ for different types of ETCs. Therefore, we quantify the relationship between maximum vorticity and ETC related precipitation in the current and idealised future climates, and also determine how this relationship depends on the structure and characteristics of the ETC. Three 10-year long aqua-planet simulations are performed with a state-of-the-art global model, OpenIFS, that differ in their specified SST distributions, which are held fixed in time. A control simulation, a uniform warming simulation and a polar amplification simulation are performed. ETCs are objectively identified using the feature tracking software TRACK and k-means clustering is applied to the ETC precipitation field to group the ETCs into clusters with similar precipitation structures. In all experiments, ETCs with stronger maximum vorticity are associated with more precipitation and this relationship is strongest in the uniform warming simulation and weakest in the control simulation. The differing slopes indicate that the increased precipitation in the warmer simulations does not feedback, via diabatic heating and potential vorticity anomalies, onto the dynamical intensity of the ETCs. The k-means clustering identifies four distinct and physically realistic types of ETCs which are present in all experiments meaning that the precipitation patterns associated with ETCs are unlikely to change in the future. The strongest relationship between ETC maximum vorticity and precipitation occurs for ETCs that have most precipitation associated with the warm front. ETCs with the heaviest precipitation along the cold front, which are the most intense storms in terms of maximum voricity, also exhibit a strong relationship between maximum vorticity and precipitation but this is weaker and with more spread than the warm front ETCs, potentially due to more convective precipitation. Not all ETC types have a strong relationships between maximum vorticity and precipitation. ETCs located at high latitudes with weak precipitation have a weak relationship due to the lack of moisture whereas ETCs with the precipitation located mainly in the centre of the ETCs have the weakest relation which is likely due to the lack of upper level forcing. These results stress that despite small changes in the strength of the cyclones, the precipitation increases are large, indicating potential future increases in flooding associated with cyclones.