The role of Warm Conveyor Belts Ascent in Modulating Atmospheric River Characteristics and Cyclone Interaction: a composite analysis

A large amount of work has been devoted to identifying and characterizing the main drivers associated with Extreme Precipitation Events (EPEs). Among these drivers the main ones are Extratropical Cyclones (ETCs) and in particular their Warm Conveyor Belts (WCBs) and Atmospheric Rivers (ARs). These features can be intrinsically linked to the other through powerful feedbacks involving moisture, latent heat, and potential vorticity.

This study aims to increase the understanding of the intricate association between ARs, WCBs, and ETCs in driving EPEs on the North Atlantic basin through a comprehensive composite analysis. Using ERA-5 data from 1979 to 2023, we investigate first the characteristics of ARs based on their interaction with the ascent phase of WCBs, a key mechanism for moisture uplift and precipitation generation within ETCs. Results show that the influence of the ascent phase intensifies the precipitation values within the AR, and that those values extend northwestward towards the cyclone location. This clearly shows the influence of the ascent phase on the precipitation generation within both ARs and ETCs.

We then develop a composite analysis of AR cases, examining the evolution of meteorological fields at 12-hour intervals from 24 hours prior to the maximum deepening point (MDP) of the associated ETC, until 24 hours after this point. This detailed temporal analysis provides insights into how the structure and intensity of ARs and WCBs evolve in relation to the dynamic development of ETCs, which is critical for understanding extreme weather phenomena (e.g., EPEs). Results show that the moisture content within the AR is at its peak on the MDP timestep, and that the precipitation values start within the AR but as the ETC develops, the pattern extends northwestward (coinciding with the ascent phase occurrence composite), with the highest values occurring also at the MDP timestep.

These results suggest that WCB-influenced ARs are characterized by a more intense and focused precipitation core, well aligned with the cyclone’s warm sector, and exhibiting a stronger coupling with cyclone deepening. This research will contribute to a more comprehensive understanding of the link between the three systems, potentially improving their predictability and supporting more effective flood and landslide mitigation strategies. Such insights are vital given the increasing frequency and intensity of extreme weather events in a changing climate.

This work was supported by the Portuguese Fundação para a Ciência e Tecnologia, FCT, I.P./MCTES through the project AMOTHEC (DRI/India/0098/2020) with DOI 10.54499/DRI/India/0098/2020 and also through national funds (PIDDAC): LA/P/0068/2020 - https://doi.org/10.54499/LA/P/0068/2020, UID/50019/2025, https://doi.org/10.54499/UID/PRR/50019/2025, UID/PRR2/50019/2025. Tiago M. Ferreira was supported by FCT through PhD grant UI/BD/154496/2022.